This paper presents a musculoskeletal percussion robot equipped with variable stiffness joints driven by pneumatic artificial muscles (PAMs). To replicate human-like single-stroke drumming, we use deep reinforcement learning in simulation and transfer the learned control strategy to real hardware. The robot’s wrist joint is actuated antagonistically, while the grip joint incorporates a single PAM to modulate stiffness. This design enables dynamic adjustment of joint stiffness and striking force. Experimental results show that both wrist elevation and grip joint stiffness significantly influence strike intensity. The successful sim-to-real transfer validates the proposed approach, offering a pathway to nuanced robotic musical performance.

Deep vein thrombosis (DVT) is a disease in which blood clots form in the deep veins of the lower limbs. It is a common condition particularly for wheelchair and bedridden patients due to prolonged sitting and supine positions. Calf compression and ankle exercises can prevent DVT, and current studies aim to combine them. However, existing devices suffer from low user comfort because of their exoskeletal structure, which consists of a rigid frame. In addition, the devices have not been tested in various positions, such as sitting and supine positions. This study introduces a flexible DVT prevention device that combines intermittent pneumatic compression (IPC) with assisted ankle exercises, which can be used in high-risk positions. The developed prototype has an endoskeleton-type structure with soft actuators, enabling natural ankle movements while remaining lightweight. Basic characteristic experiments with the prototype demonstrated that a maximum joint range of motion of approximately 30° could be achieved with a force exceeding 50 N when combining IPC and ankle exercises in both the sitting and supine positions. Blood flow evaluation experiments further showed that the combined therapy of IPC and ankle exercises, regardless of the position, was more likely to prevent DVT than no motion or single-motion modes effectively.

Exoskeleton-type assistive device is worn directly on the person, so it is important to improve coordination. In previous studies, the authors focused on the viscosity characteristics of human joints, proposed a knee joint assist method with a wide tolerance range for misalignment between the human and the device, and confirmed the effectiveness of the method. However, in previous studies, assist torque was output based on device information, which affected the misalignment between the device and the wearer. Therefore, this study examines the assist effectiveness of a viscosity assist method using inertial measurement units (IMU s) that can be directly attached to a person. In the first experiment, we compared measurements taken by an encoder mounted on the knee joint of the device and by IMU directly attached to the person during a squatting motion, and compared the misalignment of the measurements depending on the presence or absence of a command torque to the device. As a result, we confirmed the effectiveness of the IMU in reducing the misalignment between the measurement values of the device and the wearer. In the second experiment, we proposed knee joint viscosity assist method based on IMU angular velocity data during seated movement, and verified the assist effect of the proposed method and the method proposed in the previous study by measuring surface electromyography potentials. As a result, the effectiveness of the proposed method was confirmed.

We present the development of a wearable body support device for LP gas delivery work and evaluation of the device by wearers. This study proposes a method for reducing the physical burden involved in delivering LP gas cylinders, as LP gas cylinders are transported manually. Delivery personnel must navigate stairs and narrow spaces, which make it difficult to use existing methods for reducing physical burden, such as carts. We aim to develop a device that can be used for LP gas delivery. In a previous study, we conducted a field survey. We found that the burden on delivery workers was due not only to carrying the cylinder, but also to lifting. Based on the field survey, this paper describes the development of a lifting support device that reduces the physical burden and facilitates smooth delivery. The subjective evaluations confirmed that the proposed device reduced the physical burden while providing the same ease of lifting as do conventional grasping methods. The device is designed to support lifting during delivery work and greatly supports lifting movements during delivery work.

In recent years, the sea ice in the Arctic Ocean has been decreasing due to climate change caused by greenhouse gases. Therefore, the phenomena under the sea ice must be investigated. The existing method of autonomous underwater vehicle (AUV) exploration is limited by its narrow communication and acoustic triangulation range. Therefore, digging a hole through the ice sheet is proposed to secure a communication relay system under the ice sheet. The objective of this study is to develop a robot using peristaltic motion as a system for drilling holes in sea ice. In the previous study, we determined the required specifications for the sea ice drilling robot. In this study, the excavation unit and the propulsion unit of the sea ice drilling robot are developed according to this specification. The basic characteristics of each mechanism were evaluated, and the digging performance of the excavation unit and the gripping performance of the propulsion unit were confirmed.

In this paper, we describe the development of short-fiber oriented rubber and its application to elongation-type actuators. Short-fiber oriented rubber, i.e., rubber containing oriented short fibers with lengths of 3 mm, has anisotropy in the direction of fiber orientation. In a previous study, it was shown that short fiber-reinforced artificial muscles made of short-fiber oriented rubber can achieve up to 17% shrinkage. However, in that study, characteristics other than the amount of shrinkage were not measured, the basic characteristics of the developed artificial muscle were unclear, and the shrinkage ratio was smaller than that for existing straight-fiber-type artificial muscle. In the present study, we developed a new method for fabricating short-fiber oriented rubber and measured the tensile characteristics in the direction of fiber orientation and vertical to the orientation direction. Moreover, we developed an elongation-type artificial muscle from the rubber sheet and measured its elongation characteristics. Test results indicated that the fabricated rubber sheet had anisotropy. They also indicated that the anisotropy increased with the fiber concentration and that the fiber restraint acted not only in the orientation direction but also in the vertical direction. Furthermore, the developed elongation-type artificial muscle was three times more anisotropic in the ratio of axial changes to diametral changes. On the basis of these results, we expect to develop an automated production method for soft actuators.

In recent years, force feedback devices have been developed to improve the reality of virtual reality (VR) experiences. However, most of the general force feedback devices target the upper limbs. By realizing force feedback to the lower limbs, it is possible to realize an experience in VR space that cannot be achieved by force feedback to the upper limbs alone. Therefore, in this study, we developed a lower limb force feedback device based on a physical model of the human lower limb. The output torque of the developed device that met the target torque by the experiment was confirmed. The device was then experimented with to determine if it could reproduce an impact force similar to that of a soccer pass as an initial study. The results suggested that even a low torque of 10 Nm could reproduce a soccer pass.

Artificial muscles are advantageous owing to dynamic stiffness; however, the drawback of this is their poor controllability. Here, a reinforcement learning-based control system is proposed and exemplified on a realistic artificial muscle-driven robot. The proposed system suppresses the modeling error, and allows to generate dynamic motion patterns that utilize the body structure and variable stiffness characteristics. As an example application, we consider drum playing. We propose a reinforcement learning-based realistic drum-playing robot. We propose a reinforcement learning-based strategy for this realistic robot and confirm its effectiveness through simulations and experiments.

For space rockets, a rotating mixer is used to produce solid fuel. However, mixing with the rotary mixer is subject to high shear forces that limit the equipment drive. In a previous study, the authors developed a new production method using a pneumatically driven peristaltic mixing pump that simulates the intestine and a sensing system with pressure and flow rate sensors. Solid rocket fuel was successfully produced by a small pump unit. In this study, mixing experiments of solid propellant consisting of several types of powders, including metal powder and highly viscous fluids were conducted using a pump unit with a volume size eight times larger than that used in the previous study. In this experiment, mixing was performed with the materials packed in a plastic bag to increase efficiency. This reduces the contact area between the rubber tube and the contents of the device. Because only part of the mixing process is reflected in the behavior of the device, it is difficult to see differences in the sensor values, and it is unknown whether existing methods can be applied. The results of the experiment showed that the existing sensing system could be used to confirm the differences in characteristics due to the mixing process based on the time series data of air pressure and flow rate. By using Gaussian mixture model, which is a type of clustering, the mixing state was roughly binary discrimination from the acquired sensor values. This suggests that it is possible to estimate the mixing degree in large pumps using existing systems.

Recently, force feedback devices have been developed to improve the virtual reality (VR) experiences. However, most conventional force feedback devices target the upper limbs. In addition to achieving force feedback to the upper limbs, realizing force feedback to the lower limbs will make it possible to realize an experience in the VR space, which would not be achieved by force feedback to the upper limbs alone. The authors have elucidated the perceptual characteristics of the human dropping sensation to present force feedback to the lower limbs. In this study, we develop a pair of wearable force feedback shoes that can realize the falling sensation in the VR space. The proposed device meets the required specifications for descent height and acceleration to render the falling sensation. Furthermore, we confirm the usefulness of the theoretical equation by measuring the basic characteristics of the developed device.

Because information transmission by force is a vector quantity with magnitude and direction, it can directly affect humans. However, most existing force feedback devices are stationary, and their movement is restricted. On the other hand, wearable force-feedback devices induce a strange feeling, as they must support the reaction force of the presented force at the body fixing part. Therefore, in this paper, we propose a posture guidance method using force feedback provided by air jets. Specifically, for table tennis movement guidance, we developed a prototype with two degrees of freedom using a table tennis racket. We also conducted a hand posture guidance experiment and confirmed that the proposed method can guide the wrist posture without disturbing the wearer's movement.

There is an urgent requirement to solve the problem of global warming. The sea ice beneath the Arctic Ocean strongly affects the global climate. However, it has not been fully explored. The range of Autonomous Underwater Vehicles (AUV) used for under-ice exploration is limited owing to their short communication range. To solve this problem, we propose a communication relay system that uses a sea ice drilling robot. We conducted excavation and gripping experiments on actual sea ice to study the parameters and control methods required to design a sea ice drilling robot. The required specifications of excavation and propulsion units were obtained from the experimental results, and a recovery method was developed to address drilling failure.

In wearable assist devices, the assumed and actual command timings are different. This discrepancy cause problems, such as a decrease in the assist effect. In this study, we focus on viscosity, which is a characteristic of human muscles, and propose viscosity assistance to solve the problems. This method outputs the torque based on the predetermined viscosity coefficient and the actual angular velocity if the torque and angular velocity of the human joints are in opposite directions. The possibility of viscosity assist is demonstrated by analyzing the seated movement, and an assist device using a magnetorheological fluid brake is developed. The assist device is driven using three command inputs: time-based, joint angle-based, and constant viscosity coefficient command inputs. Under conditions based on time and angle, the actual output deviates from the assumed value when the motion is different from the expected motion. In terms of the viscosity command, when only the constant command is used throughout the entire motion section, some subjects showed almost identical results to those expected. Even if a deviation from this assumption is indicated, the degree of agreement can be improved by switching several types of viscosity coefficients during motion.

In this study, we evaluate the dropping sensation for the development of a wearable lower limb force feedback device that can render both dropping and walking sensations. The developed device can render the dropping sensation at a smaller height than in reality by decelerating and stopping descent during the rendering of the drop image. Considering the user will be walking with the device, a smaller device height leads to better safety. The purpose of this study is to clarify the required specifications of the height of the vertical range of motion of the platform part, and the feasibility of the concept of rendering the dropping sensation. For this purpose, the dropping sensation for the difference in human acceleration time and human deceleration acceleration was evaluated. The results showed that the rendering of the dropping sensation required more than 0.41 s of descent at an acceleration of approximately 1377 mm/s2. Moreover, the dropping sensation and sense of reality were not impaired, even when the platform part of the foot was decelerated. This result indicates that the device can be made smaller.

Many haptic devices are currently being developed for human upper limbs. There are various types of force feedback devices for upper limbs, such as desktop and wearable type. However, the lower limbs absorb most of the force when standing or walking. Therefore, to render the sensation of force to the lower limbs, a device worn like a shoe to enable users to walk and have a wide range of movement and a device that provides a dropping sensation have been developed. However, both wide-area movement and a dropping sensation could not be combined in one device. Therefore, the authors propose the concept of a lower limb force feedback device that allows the user to wear it like a shoe and provides the sensation of dropping while enabling wide-area movement. In addition, as the first stage of device development, the authors evaluated the human sensation of dropping. Consequently, it was found that a relatively high sensation of dropping can be provided to a human even with an acceleration smaller than the gravitational acceleration in real space. Thus, the lower limb force feedback device to be developed in the future will allow the user to experience the sensation of dropping by using an acceleration smaller than the gravitational acceleration in real space.

Using a head-mounted display, users can immerse themselves in virtual reality space and users can via the visual recognition of virtual objects. However, users do not experience the same haptic perception when they interact with these objects, that they do with actual objects. Force feedback devices can render haptic perception. They are classified into desktop and wearable types. A wearable 1 degree of freedom force feedback device using magnetorheological fluid brake, magnetorheological clutches, and pneumatic artificial muscles has been previously developed and it was confirmed that the device can render elasticity, friction, and viscosity. In addition, a wearable 4 degrees of freedom force feedback device using magnetorheological fluid clutches and pneumatic artificial muscles that can render elasticity was also previously developed. However, it was not established that the device could render friction, and viscosity using magnetorheological fluid clutches and pneumatic artificial muscles. In this report, it is confirmed that such a device can render friction and viscosity using magnetorheological fluid clutches and pneumatic artificial muscles without the need for magnetorheological fluid brake.

In recent years in Japan, over half of all workers suffered from lower back pain. This has become a social problem that needs to be addressed. To reduce its occurrence, we developed a flexible, high-output waist assist suit called “AB-Wear” in a previous study. The AB-Wear suit can assist human motion and reduce muscular fatigue of the waist. However, the assistive forces of the device generate compressive forces on the backbone, which have adverse effects on the body. Hence, in this study, we propose an exoskeleton-type AB-Wear equipped with a compressive force reduction mechanism, called “semi-endoskeleton-type AB-Wear”. This device has a reduction mechanism similar to a flexible flat spring behind the upper body. Because of this structure, this device can generate an effective assistive force. First, we explain the difference between the semi-endoskeleton-type AB-Wear and the previous device. Then, we model the semi-endoskeleton-type AB-Wear because the model is used for its operation. Moreover, its effectiveness is confirmed using musculoskeletal simulation. Finally it is evaluated by measuring surface electromyography (EMG) on a subject's body to confirm its effectiveness with a real body. The EMGs of the wearer with and without the suit are compared. The usefulness of the AB-Wear is confirmed by simulation and experiment.

In this study, a variable viscoelastic joint system comprising antagonized artificial muscles and magneto-rheological fluid brakes is proposed. This system enables human assisting devices such as robotic exoskeletons to retain structural softness when compared with the existing devices driven by motors and reduction gears, which can only achieve superficial softness. The authors had proposed the system and showed its effectiveness via experiments using a prototype with one degree of freedom in their previous works. In this study, as the next step in designing the human assisting device, a lower body assistive prototype “Airsist” is introduced. In addition, a control method that can cooperate with the wearer without the need for an additional operation is proposed.

A range of pneumatically-driven devices have been developed. However, these require a large air compressor, making them heavy, bulky, and therefore inappropriate for use in portable devices. In this study, we proposed and tested a portable pneumatic power source using the chemical reaction between sodium bicarbonate and citric acid. The carbon dioxide generated in the reaction was used as a pneumatic power source. The chemicals used are inexpensive, nontoxic, and readily available. From the result of basic experiment demonstrated in this paper, we conclude that the method can provide enough high pressure (more than 1 MPa) for activating pneumatic actuators and the chemical reaction is safe since it is endothermic reaction. We also demonstrated a novel system that provides continuous mixing of the reagents, using a pressure booster. The system keeps a pressure inside of a tank moderate, and tank can become light weight because it doesn't need to endure high pressure.

In this paper, permissible resistant torque considering back-drivability is verified to develop a wearable assist suit (WAS). The WAS has a clutch and a variable viscoelasticity joint. In this paper, permissible resistant torque is defined as torque that is acceptable in daily use. As first stage of the WAS development, the paper discusses the relationship between the resistant torque to the knee and the degree of discomfort experienced by the wearer as evaluated through a survey questionnaire experiment. In addition, the influence of the resistant torque on a muscle of the knee extension is considered and confirmed by measuring surface electromyography (surface-EMG).

In this study, a variable viscoelastic joint system with a clutch for a human assistance was proposed. The variable viscoelastic joint system comprised antagonized artificial muscles and magneto-rheological fluid brake (MR-brake). This system enabled the human assisting device such as exoskeletons to retain structural softness when compared with the existing devices driven by motor and reduction gear, which could only achieve superficial softness. In addition, a clutch system that provided high back-drivability to the wearer by structurally separating the device from the wearer was proposed. As an initial step in designing the human assisting device, a prototype with the proposed variable viscoelastic joint system for knee assistance is developed. Also, its control method were developed. Furthermore, experiments were conducted to confirm the influence of the proposed viscoelastic joint system on the wearer and the effectiveness of the clutch system.