Development of an SMA-Driven Tactile Keytop with Localized Micro-Vibration Pattern Rendering for Eyes-Free Keyboard Operation

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For eyes-free operation of input interfaces, tactile feedback is increasingly recognized as an important means of transmitting intuitive information. In particular, auxiliary keypads designed for creators such as illustrators and designers can cause fatigue and input errors during prolonged use. To address these issues, we propose a tactile device that delivers input feedback directly through a single keytop. Conventional haptic actuators, such as eccentric rotating mass motors (ERMs) and linear resonant actuators (LRAs), have limitations, including vibration of the entire structure in which they are installed and operational noise. Therefore, in this study, we adopted shape memory alloy (SMA) wire actuators to achieve localized stimulation and silent operation. By integrating three SMA actuators into a keytop, the proposed tactile keytop can present various types of feedback to users. The vibration characteristics of the SMA actuator were analyzed using a high-speed camera, and the results confirmed stable micro-vibration control. User experiments confirm high recognition accuracy in the tactile presentation of both spatial directional patterns and temporal rhythm patterns. In addition, qualitative evaluations demonstrate that driving frequency adjustment enables the presentation of a diverse range of tactile sensations. These findings indicate that the proposed tactile keytop has potential as a localized tactile feedback interface for future eyes-free input systems.