Past Research

• Active Bone-Conducted Sound Sensing for Estimating Joint Angle

We propose a wearable sensor system that measures joint angles of an elbow and finger using vibration which is emitted actively.  A novelty of this research is to use active sensing for measuring a joint angle.  The active sensing means to emit vibration and sounds to a bone, and a microphone receives the propagated vibration and sounds.

• Haptic-enabled Active Bone-Conducted Sound Sensing

We propose active bone-conducted sound sensing for estimating a joint angle of a finger and simultaneous use as a haptic interface. For estimating the joint angle, an unnoticeable vibration is input to the finger, and a perceptible vibration is additionally inputted to the finger for providing haptic feedback. The joint angle is estimated by switching the estimation model depending on the haptic feedback and the average error of the estimation is within about seven degrees.

• Hand Pose Estimation based on Active Bone-Conducted Sound Sensing

Estimating hand poses is essential to achieve intuitive user interfaces. In Virtual Reality, an infrared (IR) camera is used for hand tracking, and direct manipulation can be accomplished by using hands. Additionally, wearable devices have also attracted attention because of their portability. We have developed a method based on the use of a wearable device to estimate the joint angle, which can be determined using the amplitude of vibration. However, the joint angle, which can be estimated, is limited to particular joints. Therefore, our proposed method determines the hand pose based on active bone-conducted sound sensing toward intuitive user interfaces. We employed the power spectral density as a feature, thereby enabling the hand pose to be classified with a support vector machine. We confirmed the recognition accuracy and the feasibility of our proposed method through evaluation experiments.

• Estimating contact force of fingertip

This study proposes a method for estimating the contact force of the fingertip by inputting vibrations actively. The use of active bone-conducted sound sensing has been limited to es- timating the joint angle of the elbow and the finger. We ap- plied it to the method for estimating the contact force of the fingertip. Unlike related works, it is not necessary to mount the device on a fingertip, and tactile feedback is enabled using tangible vibrations.

• Grip Force Estimation based on Active Bone-Conducted Sound Sensing

We propose a method for determining grip force based on active bone-conducted sound sensing, which is an active acoustic sensing. In our previous studies, we estimated the joint angle, hand pose, and contact force by emitting a vibration to the body. We aspired to expand to an additional application of an active bone-conducted sound sensing, thus, we tried to estimate the grip force by creating a wrist-type device. The grip force was determined by using the power spectral density as the features, and gradient boosted regression trees (GBRT). Through evaluation experiments, the average error of the estimated grip force was around 15 N. Moreover, we confirmed that the grip strength could be determined with high accuracy.

• Contact Point Estimation using Pneumatic System Noise

Active acoustic sensing is being widely used in various fields, with applications including shape estimation of soft pneumatic actuators. In a pneumatic system, air tubes are frequently adopted, and thus it is essential to detect failures along the air path. Although acoustic sensing has been used for detecting contact and identifying the contact position along a tube, it has not been applied to pneumatic systems. We devised an acoustic sensing method to this end for air tubes in a pneumatic system. As pneumatic system noise propagates through the air tube, we employed this type of noise instead of the conventional method of using a sound source or emitting vibration with an additional oscillator.