Refreshable braille-cell display implemented with shape memory alloys

Abstract

A refreshable braille cell display uses a single moving part per tactile element. Tactile elements, formed from stainless steel tubing, are assembled in densely arranged modules. Lower ends of the tactile elements extend beneath the modules and are in contact with a pressurized medium. Shape memory alloy actuators are positioned in the tactile elements, isolated from any motion or flow in the pressurized medium. When a pressurized medium is delivered through a port in a tactile element, the actuator extends upward, thereby forcing the upper portion of the tactile element through a hole in the user contact surface. In that state the tactile element indicates information. When the tactile element is activated, current flows from an electrical contact at the lower end of the tactile element, through the actuator, and into the outer tube of the tactile element. The actuator heats, due to electrical resistance, contracts and exerts a downward force on the pressure medium. The upper portion of the tactile element is drawn below the user contact surface, indicating the absence of information. Distributed pulse width modulation allows instantaneous power requirements to be minimized, and only low safe voltages are needed to operate the array. By applying a bias force to all actuators via a common reservoir of either pneumatic or hydraulic pressure, the design is simplified, and reliability is increased. When integrated with a computer, the refreshable tactile array of elements gives users access to full computer generated screens of text and graphical information in real time.