This paper presents a simple but effective way of enhancing tactile stimulus by a mechanism with springs to preserve elastic energies charged in a prior energy-charging phase and discharge them to enhance the force to hit a finger in the stimulating phase. With this mechanism, a small and light stimulator attached to the fingertip is developed and demonstrated to generate the tactile feedback strong enough to make people feel as if their fingers collide with a virtual object. It is also shown that the durations of the two phases can be as short as a few milliseconds so that the latency in tactile feedback can be negligible. The performance of the mechanism and the effectiveness of its tactile feedback are evaluated for in-air keypress and swipe operations.

When we use a tablet style handheld device such as a smart phone as a part of a virtual really system, its most outstanding future: the touch screen dominating the most area of the front face should be incorporated into the system effectively and beneficially. For example, the visual information displayed on the screen can be merged with the surrounding or background scenes and the intuitive touch operation can be performed in a suitable scenario. However, if the means of the interaction is limited to the touch operation, finger operation on the front screen must be performed even for unsuitable scenarios, and the fingers or hands occluding the visual information disturb our immersive experience. To deal with this situation, we propose a multi-modal interactive tablet that uses its cameras, accelerometer, track ball and pressure sensors implemented on its rear and side for operations ensuring visibility. The pressing and ball-rotating operation on the rear and the side and the tactile feedback generated by voice-coil-based actuators assist and guide the multi-modal interaction. The effectiveness of the multi-modality with the rear and the side operation and the tactile feedback is evaluated by an experiment.