Ishizuka Hiroki

In this study, we propose a device that can output high-frequency signals without touching the vibration source by using sound, and to improve the problem of reduced output in the low-frequency band, which is a characteristic of a speaker, I use amplitude modulation to reproduce low-frequency waves from high-frequency waves. I conducted pressure measurements to validate the amplitude modulation. The results confirmed that the modulated waves were output correctly and that the modulation increased the output in the low frequency band.

In this study, we developed a pneumatic vibrotactile display that uses sound pressure from a speaker to generate changes in air pressure, which is transmitted to the fingertip via a silicone tube to enable the presentation of vibrations over a wide bandwidth. Generally, pneumatic vibrotactile displays using air compressors have difficulty in presenting vibrations in high frequency bands, especially above 200 Hz, due to limitations in the response speed and control performance of the open/close valve. For this reason, this study attempted to construct a system that can handle a wider range of frequencies by taking advantage of the high responsiveness of the speaker. Specifically, by transmitting air pressure vibrations generated by changes in the speaker’s sound pressure to the fingertips through silicon tubes, this system enables the presentation of tactile stimuli that include high-frequency components, which has been difficult with the conventional air compressor system.

In this study, we employed a control algorithm based on the free energy principle to control the actions of a robot arm towards achieving a specified posture. By administering the robot arm in accordance with the free energy principle, we endowed the robot arm with the capacity to possess and update its perception, subsequently generating actions based on the perception. Through the minimization of errors between the sensory information predicted based on the perception and the sensory information acquired from the external environment, the robot arm can infer the state of the external world, generate actions appropriate to its body structure, and achieve the goal.

本発表では，人間の皮膚，末梢神経，中枢神経を模倣した触覚センシングシステム及び，人間の触知覚のメカニズム解明に関する取り組みについて発表する．人間の触覚知覚のメカニズムは生理学実験の結果から徐々に解明されつつあるものの，それを生体のメカニズムに基づいて完全再現するような取り組みは行われていない．そこで，皮膚の特性を模した柔軟な材料の中に受容器サイズのセンシング素子を埋め込んだ触覚センサを実現する．次に，触覚受容器の応答や中枢神経での情報処理を再現可能な数理モデルを構築し，計算機に実装する．最後に，このセンシングシステムが人間と同じ触覚を有することができるかを，例として材料識別能を評価することで明らかにする．また，このようなセンシングシステムを高度化するためには触覚だけでなく，他の感覚情報がどのようにセンシングシステムに活用されるのかを明らかにする必要もある．その一例として，触覚情報と視覚情報の脳における処理に関する研究を行っており，それについても発表する．

Sustaining a sense of adventure is important for improving the likelihood of life opportunities. In this study, we propose a wearable haptic presentation device that promotes emotional arousal with the aim of fostering an emotional state that enhances an individual's sense of adventure. We then investigate the extent to which the user's emotional state is affected by the type of tactile rhythm generated by the device. The results showed that the tactile presentation by the proposed device did not consistently change the emotional valence, but the arousal level changed with the tactile presentation rhythm. Furthermore, the results suggest the existence of rhythmic patterns that enhance cognitive states associated with adventurous attitudes such as "optimistic attitude" and " ease. The present results suggest that tactile presentation with rhythm may be able to change human emotions in a way that encourage adventure.

In this paper, we propose a composite modeling method that combines high-viscosity cure inhibitors, high-viscosity lubricants, modeling of adhesive surfaces, fiber reinforcement, and other techniques. This method allows for customization of molding characteristics to some extent by utilizing different methods, such as adding inhibitors and lubricants, incorporating fabrics, and molding surface textures. The degree of lubrication, adhesion, and tearing strength can be achieved using these techniques. In the latter half of the presentation, we demonstrate a robot finger modeled using this method, which is capable of smooth tendon-driven motion.

In this paper, we propose a method to fabricate silicone soft pneumatic actuators with different motion characteristics from the same mold. In the proposed method, the motion characteristics are controlled by forming a pattern of hard silicone on the surface of an actuator base made of soft silicone.

Soft robots have been developed in recent years. In order for a soft robot to perform complex motions, it is needed to operate multiple actuators using multiple wires. Multiple wires increase the weight of the soft robot and limits the degree of freedom. We propose a system that uses a single channel to operate a specific actuator from a group of them by combining conductive droplet spacing and electrode spacing. In this system, two electrodes facing each other across the channel are placed at different intervals to connect the actuator to the power supply. While flowing insulating fluid in the channel, multiple conductive droplets are injected at various intervals. Regardless of the order in which the actuators are placed, only those actuators with electrodes that have the same intervals as conductive droplets will operate. This method can simplify the driving system and reduce the weight of soft robots.

Tactile sensors are necessary for robots to understand surrounding environments and their states. Recently, soft tactile sensors have been widely developed to integrate them into soft robots. Although, the detection parts and substrates of many soft tactile sensors compose of soft materials such as silicone rubber and liquid metal, stiff components such as electrical elements and wires are also embedded. The stiff embedded components reduce flexibility and durability. In this research, we develop a soft capacitive tactile sensor using the movement of interface between encapsulated air and water in a silicone rubber body. A force applied to the tactile sensor causes a change in the position of the interface. Displacement of the interface changes the capacitance of the sensor. The structure does not require an ohmic connection between a contact and a detection part and improves durability.

In recent years, soft tactile sensors comprising liquid metal and silicone rubber have been studied for tactile sensing of soft robots. In order to obtain detailed information about objects, the sensor array was configured by utilizing crossing of orthogonal microchannels filled with liquid metal as sensing elements in previous research. In this study, we propose the soft tactile sensor array with independent sensing elements. This sensor embeds narrow microchannels standing vertically in silicone rubber. Microchannels are filled with liquid metal and used as sensing elements. This structure realizes miniaturization and high-density placement of sensing elements while maintaining the independence of the sensing elements. We fabricated the sensor with 16 sensor elements of 0.4mm width embedded at 2.0mm intervals.

Pneumatic actuators have been applied to wearable haptic devices owing to their lightweight. However, the pneumatic actuators require an air compressor and air valves. Thus, the resulting systems are large and heavy. We have studied a haptic display using a liquid-to-gas phase change actuator. The actuator is composed of a thin plastic pouch containing a low boiling point liquid. A Peltier device controls the temperature of the liquid in close contact with an actuator. In this study, we embedded a small pressure and temperature sensor in the actuator and measured the pressure change induced by heating. The result indicates that the maximum pressure in the actuator is determined by vapor pressure, and a few tens of seconds are required to reach the maximum pressure.

Biometric authentication such as face recognition and fingerprint recognition have been pervasive. However, there are many attacks against the biometric authentication. One of them is a "presentation attack" using artificial biometrics to break the authentication. Meanwhile, several approaches using photoplethysmogram (PPG) which can be recorded optically for authentication have been proposed. PPG-based authentication may be available in the near future, because PPG have fewer restrictions in measurement sites and postures than other biometrics, and smartwatches with PPG recording function have been pervasive. Therefore, the prediction of attacks against PPG-based authentication and countermeasures are required. We proposed a presentation attack using the advantage of PPG in performing measurements on various sites. The attack records PPG stealthily and utilizes it for identity spoofing. We investigated the feasibility of the attack and showed that the attack may occur. We investigate countermeasures using the unique information of the measurement sites against the attack.

Force sensors such as load cells are used to measure the force applied to the skin when an object comes into contact with it. However, it is very difficult to measure the distributed stress inside the skin with these sensors. To solve this problem, we propose a method to measure the stress inside the skin by using the color change when pressure is applied to the skin. In order to investigate the effectiveness of this method, we measured the color change of the skin and the distribution of the stress in the skin using the finite element method when the cylindrical stimulus was pressed. This method is expected to make it possible to measure body pressure without contact and to include internal stress.

For early detection of the slight muscle injury, we present a sensing method based on electrical impedance distribution of musculoskeletal tissue. The system collects potential data for various excitation conditions by using multiple electrodes surrounding the target object and discriminates the muscle state by machine learning. We optimize the sensing efficiency by selecting excitation conditions based on the correlation analysis of the normal and injured muscle. We utilize the simulated data for optimizing the parameters of discriminator without using measurement data for the injured state. Furthermore, we propose an environment-invariant detection method by considering implementation error of the electrode position. We investigated the effective excitation conditions and discrimination ratio by using a musculoskeletal phantom for various injured conditions. As a result, it was found that the proposed system has 100 % discrimination ratio using 7 out of 120 excitation conditions and reduced measurement time from 38.4 s to 224 ms.

To develop a simple and accurate measurement technique of intramuscular fat, we present a new sensing method based on the change in the electrical impedance by muscle stretch. The system obtains the electrical gain characteristics of the muscle tissue for various stretch conditions, and identifies the parameters by fitting the transfer function of the equivalent circuit to the obtained data. Then, the amount of intramuscular fat is estimated by the multiple regression model using the parameters. For the feasibility evaluation, we investigated the estimation error by using a phantom that mimics the electromechanical properties of muscle and fat. As a result, we found that the proposed system is capable of estimating the fat amount with 2.7 % error. Because the estimation error of the sensing method without muscle stretch conditions was 5.6 %, the use of muscle stretch was found to be effective for reducing the estimation error.

It is important for the softness/hardness presentation of the fingertip to design of the contact part in the softness/hardness presentation device. In this study, we used shape changing airbag by air volume for contact part of the force feedback device. We examined the relationship between the contact area and the air volume for the four air bag structure and evaluated the effectiveness for the softness/hardness presentation. As a result, we found that the elliptical airbag with a single inflated part behaved similarly to the human perception curve and showed satisfactory characteristics for the expression of the contact area.