Smart rings can serve as a wearable platform for off-device control of nearby devices. However, their thin bands lead to a small touch surface on the ring, limiting touch input expressivity and accuracy. To address this, we investigate the effectiveness of ring shapes that use beveled surfaces in addition to the flat outer surface as input surfaces. The distinct angles of the three surfaces limit touches to the intended surfaces, improving accuracy. A first study showed that with band widths of 6 mm or less, flat rings achieved low accuracy (63.8%) in distinguishing between left and right edge touches, whereas beveled and rounded rings achieved high accuracy (90.0%, 93.3%). In a second study of nine touch gestures on 6-mm rings, beveled rings outperformed the flat rings, achieving 92.9% (sighted) and 91.8% (eyes-free) with FPR \(\le 1\%\). Through these investigations, we identify beveled surfaces as a promising method toward expressive, precise touch input.

Fingertip force control plays an important role in learning motor skills. Exoskeleton gloves have been developed to assist with fingertip force control, but having the equipment on the fingers interferes with finger motion control and tactile sensation. Thus, we present a system for assisting with voluntary fingertip force control that does not require any devices to be worn on the fingers. In this study, we focused particularly on lateral pinch force, which is grip force achieved with the pad of the thumb and the lateral surface of the index finger to grasp objects. We use active bio-acoustic sensing to estimate voluntary pinch force with piezo elements attached to the back of the hand and electrical muscle stimulation (EMS) to the forearm to control involuntary pinch force in a closed-loop system. We developed three prototypes and conducted user studies to investigate whether our system can assist with pinch force control under several target forces, from weak to strong. Our user studies showed that the combination of active bio-acoustic sensing and EMS can assist users in maintaining the pinch force closer to the target force.

When playing scales on the piano, playing all notes evenly is a basic technique to improve the quality of music. However, it is difficult for beginners to do this because they need to achieve appropriate muscle synergies of the forearm and shoulder muscles, i.e., pressing keys as well as sliding their hands sideways. In this paper, we propose a system using electrical muscle stimulation (EMS) to teach beginners how to improve their muscle synergies while playing scales. We focus on “thumb-under” method and assist with it by applying EMS to the deltoid muscle. We conducted a user study to investigate whether our EMS-based system can help beginners learn new muscle synergies in playing ascending scales. We divided the participants into two groups: an experimental group that practiced with EMS and a control group that practiced without EMS. The results showed that practicing with EMS was more effective in improving the evenness of scales than without EMS and that the muscle synergies changed after practicing.

We explore how to design emotional expression using tabletop social robots with multiple texture modules. Previous studies in human-robot interaction have presented various designs for emotionally expressive robots without using anthropomorphic forms or cues. They revealed that haptic stimulation based on the textures and movements of the robots could evoke some emotions in users, although these were limited. In this work, we propose using a combination of textures and movements for richer emotional expression. We implemented tabletop robots equipped with detachable texture modules made of five different materials (plastic resin, aluminum, clay, Velcro, and cotton) and performed a user study with 13 participants to investigate how they would map the combinations of textures and movements to nine emotions chosen from Russell's circumplex model. The results indicated that the robots could express various emotions such as excited, happy, calm, and sad. Deeper analysis of these results revealed some interesting relationships between emotional valence/arousal and texture/movement: for example, cold texture played an important role in expressing negative valence, and controlling the frequency of the movements could change the expression of arousal.

In this paper, we propose to use facial electrical stimulation to control maximal voluntary contraction (MVC) of the upper limbs. The method is based on a body mechanism in which the contraction of the masseter muscles enhances MVC of the limb muscles. Facial electrical stimulation is applied to the masseter muscles and the lips. The former is to enhance the MVC by causing involuntary contraction of the masseter muscles, and the latter is to suppress the MVC by interfering with voluntary contraction of the masseter muscles. In a user study, we used electromyography sensors on the upper limbs to evaluate the effects of the facial electrical stimulation on the MVC of the upper limbs. The experimental results show that the MVC was controlled by the facial electrical stimulation. We assume that the proposed method is useful for sports athletes because the MVC is linked to sports performance.

Muscle fatigue monitoring is important for injury prevention in sports. Previous studies have shown that wearable electromyography (EMG) sensors on limb muscles can be used to monitor the level of muscle fatigue continuously. However, there are two main problems in using these sensors for sports. One is that users wearing them create motion artifacts that affect the sensor data. The other is that the sensors disturb limb motion. To address these problems, we propose a method for estimating biceps fatigue with an e-textile headband. There is a strong correlation between frowning and jaw clenching muscle activity and the physical efforts made when exercising. Our method uses both of EMG signals of the temporal muscles and motion artifacts. The former indicate jaw clenching and the latter indicate frowning. Experimental results show that the root mean square values calculated from the headband sensor values significantly increased when biceps were fatigued.

In augmented reality (AR) environment, tactile stimuli as if a user touched virtual objects are important for realizing natural interactions. Most previous works employ tactile devices such as vibration actuators. However, the place where the system can stimulate a user depends on the place which is covered by the devices. In addition the accuracy of user's tactile perception is low, so it is difficult to present tactile feedback at intended locations. The purpose of this study is to establish a method that represents smooth two-dimensional tactile moving strokes independent of locations of the tactile devices. Our aim is to let a user perceive that locations of vibrotactile perception are on those of visual stimuli. Thus we can present tactile feedback in larger places with higher resolution by controlling visual stimuli. In this paper we have investigated the correlation between visual stimuli and tactile perception. The results of experiments showed that visual stimuli can induce tactile illusion, which resembles the position of virtual objects.