Ungrounded Haptic Augmented Reality System for Displaying Roughness and Friction

This paper presents the design and validation of an ungrounded haptic augmented reality system that alters the roughness and friction of a rigid 3-D object. The user touches the object via a custom haptic stylus; the stylus tip is a ball mounted in a socket that has low internal friction and produces minimal vibrations, necessary conditions for creating a haptically clean interaction. We determine contact position and force using a six-axis force/torque sensor beneath the object. The object's apparent roughness and kinetic friction are altered using haptic models that we previously created from real tool-surface interaction data. The textural roughness model generates a vibration waveform in real time, which is played through a voice coil actuator. A solenoid inside the stylus applies a braking force to the ball for friction rendering. The friction model continually controls the solenoid current, setting the effective kinetic friction coefficient between the stylus tip and object surface to values between 0.20 and 0.52. Analysis of commanded and displayed haptic signals verifies that this system accurately overlays the modeled roughness and friction on the object's geometry, providing a significantly better match than the same models rendered using a Phantom Omni.