A Refreshable Braille Cell Based on Pneumatic Microbubble Actuators

A refreshable Braille cell as a tactile display prototype has been developed based on a 2 x 3 pneumatic microbubble actuator array and an array of commercial valves. The microbubble actuator acting as a Braille dot consists of a parylene corrugated diaphragm and an overcoated elastomer layer. Polyurethane (PU) and polydimethylsiloxane (PDMS) elastomer-based Braille cells were fabricated and compared in terms of their displacement-pressure characteristics, force-displacement characteristics, dynamic response, and hysteresis of elastic deformation. Both PU- and PDMS-based pneumatic Braille cells demonstrate satisfactory properties against the static and vibrational tactile display requirements. The displacement of the PU-based Braille dot is 0.56 mm at a 0.2-Hz operating frequency, and the generated force is 66 mN at a 100-kPa applied pressure. The strong hysteresis observed in microbubble actuators made with PU elastomer is resolved by the use of PDMS elastomer. The refreshable Braille cell was also designed to meet the criteria of lightness and compactness to permit portable operation. The design is scalable with respect to the number of tactile actuators while maintaining fabrication simplicity.