Combining Haptic Augmented Reality with a Stylus-Based Encountered-Type Display to Modify Perceived Hardness

Simulating realistic hard objects in virtual environments using a force-feedback haptic device is essential for many tasks. Traditionally these objects have been rendered using position-based or event-based methods, but these methods cannot match the hardness of real objects. We propose a new method to render hard objects by combining augmented reality and a stylus-based encountered-type haptic display (ETHD) using a modified haptic device to independently render stiffness and hardness. Stiffness is rendered by the motors of the device, and hardness is rendered by attaching a plate with a carefully-chosen hardness to the device's end-effector. This paper compares our method to traditional rendering methods (spring and spring-damper position-based models, and acceleration matching event-based haptic models) for rendering soft, medium, and hard objects. Our results show that our ETHD method created the most realistic objects among the rendering methods tested. The perceived hardness rendered with the ETHD was always higher than other methods, and most people preferred the ETHD device over traditional methods.