Adding Tangential Forces in Lateral Exploration of Stiffness Maps

We believe that the lateral exploration of surfaces with varying stiffness, stiffness maps, using computer generated haptics is an underestimated and important procedure with impact in many application areas. Feeling the change of stiffness while sweeping the haptic probe over a surface can potentially give an understanding of the spatial distribution of this stiffness, however current algorithms lack tangential cues of stiffness changes. This introduces energy sources and sinks that potentially affects the stability of the system, apart from being physically incorrect and thus unrealistic. We discuss the forces and effects involved in the exploration of stiffness maps and propose an energy-based algorithm for tangential forces that augments the feedback from the map, in particular during lateral exploration. The algorithm is based on basic physical principles and has the potential to increase both realism and stability. A user study was conducted to analyze the effect of this algorithm on stiffness perception.