Design and Evaluation of a 3-DoF Haptic Device for Directional Shear Cues on the Forearm

Wearable haptic devices on the forearm can relay information from virtual agents, robots, and other humans while leaving the hands free. We introduce and test a new wearable haptic device that uses soft actuators to provide normal and shear force to the skin of the forearm. A rigid housing and gear motor are used to control the direction of the shear force. A 6-axis force/torque sensor, distance sensor, and pressure sensors are integrated to quantify how the soft tactor interacts with the skin. When worn by participants, the device delivered consistent shear forces of up to 0.64 N and normal forces of up to 0.56 N over distances as large as 14.3 mm. To understand cue saliency, we conducted a user study asking participants to identify linear shear directional cues in a 4-direction task and an 8-direction task with different cue speeds, travel distances, and contact patterns. Participants identified cues with longer travel distances best, with an 85.1% accuracy in the 4-direction task, and a 43.5% accuracy in the 8-direction task. Participants had a directional bias, with a preferential response in the axis towards and away from the wrist bone.