SensARy Substitution: Augmented Reality Techniques to Enhance Force Perception in Touchless Robot Control

The lack of haptic feedback in touchless human-robot interaction is critical in applications such as robotic ultrasound, where force perception is crucial to ensure image quality. Augmented reality (AR) is a promising tool to address this limitation by providing sensory substitution through visual or vibrotactile feedback. The implementation of visual force feedback requires consideration not only of feedback design but also of positioning. Therefore, we implemented two different visualization types at three different positions and investigated the effects of vibrotactile feedback on these approaches. Furthermore, we examined the effects of multimodal feedback compared to visual or vibrotactile output alone. Our results indicate that sensory substitution eases the interaction in contrast to a feedback-less baseline condition, with the presence of visual support reducing average force errors and being subjectively preferred by the participants. However, the more feedback was provided, the longer users needed to complete their tasks. Regarding visualization design, a 2D bar visualization reduced force errors compared to a 3D arrow concept. Additionally, the visualizations being displayed directly on the ultrasound screen were subjectively preferred. With findings regarding feedback modality and visualization design our work represents an important step toward sensory substitution for touchless human-robot interaction.