Naohisa Nagaya

Presenting virtual stiffness by modulating the perceived force profile with suction pressure

This paper reports a study on modulating the perceived stiffness by controlling the perceived force evoked from suction pressure stimuli. It demonstrates an early attempt of using suction pressure stimuli for augmenting the perceived stiffness of a spring. The purpose of this work is twofold; 1) to validate a requirement needed for the device in force enhancement applications, 2) to tentatively explore the effect of suction pressure stimuli on stiffness perception. In this study, we used physical springs for the stiffness stimuli, and a tool (tactile interface) was used for stiffness exploration. Human subjects were requested to explore and estimate the stiffness of a spring sample. Suction pressure stimuli were applied on the contact areas between the finger the tool during stiffness exploration. The amount of suction stimuli adjusts correspondingly with the measured force, but it is regulated by a psychophysical function. We introduced the gain to scale the measured force, thereby adjusting the profile of the pressure stimuli. We found that the perceived stiffness of the spring appears to increase with higher gain. The result seems to suggest that stiffness augmentation is feasible by modulating the stiffness perception using multipoint suction pressure stimuli.

Haptic cue of forces on tools: Investigation of multi-point cutaneous activity on skin using suction pressure stimuli

This paper presents an initial data that could show a possible contribution of mechanoreceptor activity to the perception of forces applied on grasped objects. Here, we obtained detailed psychophysical characteristics of perceived force-magnitude in multiple degrees of freedom (MDOF) using multi-point suction pressure stimuli. To obtain such data, we developed a multi-point stimulation method that can represent MDOF perceived force on a tool. We characterized the perceived force response of human subjects to suction pressure stimuli through psychophysical experiments. Moreover, we analyzed the strain energy density (SED) on the finger pads considering the force applied through finite element simulation. The results of the psychophysical experiments showed that multi-point stimulation method is effective for evoking MDOF perceived force on a tool. Interestingly, we found that the results of the finite element analysis agree with those of the psychophysical data. Therefore, we have verified that it is possible to use multi-point suction pressure stimulation for representing perceived force on objects held in a hand. In addition, a preliminary insight into the role of SED for perceiving force on tools is provided.

A precise gait phase detection based on high-frequency vibration on lower limbs

A novel gait phase detection method that can extract the timing of foot contact conditions (Heel Strike and Toe Off) by a single piezo film sensor attached on each leg is proposed. We focused on the occurrence of high-frequency vibrations (> 100 Hz) in the beginning and the end of stance phases during gait. After the features of vibration waveforms during gait were confirmed, we proposed the phase detection method. The optimal parameters were investigated to detect the phases robustly despite the walking speed and the shoe types. Experimental results showed that the detected ground contact events had high accuracy of timing. Finally, we confirmed the feasibility with the prototype wearable device in usual environments.

Multi-contact vacuum-driven tactile display for representing force vectors applied on grasped objects

In this paper we demonstrate an idea of multi---point tactile stimulation for representing force illusions on hand-held objects using vacuum pressure stimuli. The device used for the demonstration is pen-based and it is held by the fingers and thumb in a precision grip. There are two types of these devices; a three degree of freedom and a five degree of freedom tactile interfaces. These degrees of freedom are essentially illusions observed from the tactile stimuli. The initial prototype is capable of displaying force-like sensations in the three basic coordinate axes and moment-like sensations along two axes.