With the emergence of augmented and virtual-reality based information delivery technologies the gap between availability of communication devices for visually impaired people and sighted people is emerging. The current study describes a communication tool which provides a reading platform for visually impaired people by means of a haptic display. In this paper the development and human subject study based evaluation of an electromagnetic microactuator-array based virtual tactile display is presented. The actuator array is comprised of a 4 by 5 array of micro voice-coil actuators (tactors) providing vibrotactile stimulation on the user’s fingertip.
The size and performance of the actuators is evaluated against the thresholds of human tactile perception. It is demonstrated that a 2.65 mm (diameter) × 4 mm (height) generic tactor is suitable for practical applications in dynamic tactile displays. The maximum force of the actuator was 30 mN generated at current levels of 200 mA. At a stroke of 4.5 mm, the force is reduced to 10 mN. The peak force was generated at a displacement of 1.5 mm.
A total of 10 alpha-numeric symbols were displayed to the users via dynamically changing the location of the vibrating point in a predefined sequence, thus creating a tactile perception of continuous curve. Users were asked to sketch out the perceived symbols. Each subject carried out three experiments. The first experiment exposed all subjects to ten different characters. Data obtained from human subject tests suggest that users perceive most shapes accurately, however the existence of jump discontinuities in the flow of presentation of the curves lowers recognition efficiency most likely due to loss of sensation of solid reference point. Characters containing two or more discontinuous lines such as ‘X’ were more difficult to recognize in comparison to those described with a single line such as ‘P’, or ‘Z’. Analysis of the average character recognition rate from 10 volunteers concluded that any presented character was identified correctly in 7 out 10 tests. The second test included characters that were reused from the first experiment. Users had improved their character recognition performance as a consequence of repeated exposure and learning. A final set of experiments concluded that recognition of groups of characters, forming words, is the least efficient and requires further perfecting. Recommendations for improvements of the recognition rate are also included.