Fractional models improve realism of touch feedback for viscoelastic materials
Perceptual Comparisons of Viscoelastic Renderings: Fractional- vs Integer-Order Models
Robotics
Summary
Touching soft materials often feels different because their squishiness changes over time. The paper shows that using a special kind of math model called fractional-order models can make virtual touch feel more like real materials. The authors tested these models against older ones by asking people which felt more real. People consistently found the fractional models gave a better sense of realistic touch.
What this means in practice
- •For haptic device developers: Improve the realism of touch sensations in devices that simulate soft materials by using fractional-order viscoelastic models.
- •For virtual reality developers: Enhance tactile feedback in VR environments to better mimic how soft materials behave over time using perceptually optimized fractional models.
Authors
Gorkem Gemalmaz, Harun Tolasa, Volkan Patoglu
Abstract
Realistic haptic rendering of viscoelastic materials requires reproducing time-dependent behaviors such as creep and stress relaxation, which arise from the material's inherent memory effects. Fractional-order viscoelastic models have been shown to capture these dynamics accurately and compactly, but it remains unclear whether their increased fidelity translates into perceptual benefits during haptic interaction. In this work, we investigate whether users perceive fractional-order models as more realistic than conventional integer-order models while rendering viscoelastic materials. We compare the fractional-order standard linear solid (FO-SLS) model with two integer-order alternatives: the 3-parameter SLS model and the 5-parameter generalized Maxwell model. We consider two complementary approaches to optimal parameter selection to evaluate rendering realism from both objective and perceptual perspectives: In the first approach, we determine the model parameters via least-squares based system identification of physical viscoelastic reference materials to establish evaluation baselines. In the second approach, we determine population-level perceptually optimal parameters using a qualitative-feedback-based human-in-the-loop optimization and aggregation method. This method establishes model parameters that maximize perceived realism of viscoelastic behaviors through qualitative evaluations. Human-subject experiments indicate that the FO-SLS model is perceived as significantly more realistic than both integer-order alternatives under both parameter selection approaches. Overall, this study provides experimental evidence that fractional-order viscoelastic models are not only theoretically well-motivated, but also perceptually relevant for realistic haptic rendering of creep- and relaxation-dominated behaviors of viscoelastic materials.