Modeling Pneumatic Actuators for a Refreshable Tactile Display

In this paper, we develop a dynamic lumped parameter model of a pneumatic membrane actuator to inform the design of a shape display that meets force, speed and spatial density specifications for refreshable braille. A system identification experiment is undertaken to determine relevant system parameters that remain fixed under variation of the lengths of the connecting tubes and cavity volumes. Parameter values were found to fit a numerical solution to a step response in pressure for multiple line lengths. Two additional experiments were conducted using various applied pressures and actuator cavity volumes to validate the model. Extrapolation of the model to the dimensions of a first prototype scaled at 5/3 braille dot size and spacing predicts a 1.4 Hz bandwidth whereas experiments yield a 1.7 Hz bandwidth.