Perception of a Haptic Jamming display: Just noticeable differences in stiffness and geometry

This work characterizes aspects of human perception of a Haptic Jamming device, a tactile display capable of simultaneously and independently controlling its stiffness and geometry via particle jamming and pneumatic actuation. A single Haptic Jamming cell is filled with coarse coffee grounds, connected to vacuum, and placed over a pressure-regulated air chamber. Increased vacuum level in the cell increases cell stiffness, and increased pressure in the chamber beneath the cell balloons the cell upward. Single-cell devices were manufactured and tested to determine the relationships between the vacuum and air pressure levels and the device outputs, stiffness and geometry, respectively. Using these relationships, reference and comparison values were selected for each output, and psychophysical experiments were conducted to determine the Weber Fraction for rigidity (an alternate terminology for nonlinear stiffness, used in the experiment prompt) and geometry, represented by the eccentricity of the elliptical profile of the cell. The Weber Fractions for stiffness and geometry were 16.0% and 14.3%, respectively. No significant correlation was found between human perception of these stimuli and the forces/torques applied to the devices during haptic exploration. These results will enable more accurate representations of virtual environments using an array of haptic jamming cells under development for medical training and simulation.