Haptizing Surface Topography with Varying Stiffness Based on Force Constancy: Extended Algorithm

This article introduces a novel haptization method for rendering surface topography with varying stiffness via a force-feedback haptic interface. Previously, we showed that when surface topography with varying stiffness is rendered with the conventional penalty- based method, topography information perceived by the user can be distorted from its model. This phenomenon was explained by the theory of force constancy which states that the user maintains an invariant contact force level when s/he strokes a surface to perceive its topography. To resolve the problem, we then developed a basic topography compensation algorithm (TCA) based on the force constancy, for a single height-change region with nonuniform stiffness perceived via lateral stroking. The basic TCA was mainly to test the applicability of force constancy to haptic rendering. In this article, we present an extended TCA that adequately delivers surface topography that may contain a number of height-changing regions with varying stiffness for any user exploratory patterns. We also measured the human detection thresholds of surface slope mediated with a force-feedback device and used these data for designing the extended TCA. The performance of the extended TCA was extensively examined in terms of proximal stimuli it creates and actual percepts induced from the stimuli. The extended TCA brings a one-step advance from the current practice of haptic rendering which requires constant surface stiffness for an adequate delivery of surface shape.