The synthesis of three dimensional haptic textures, geometry, control, and psychophysics

The synthesis and rendering of haptic textures is extremely sensitive to the characteristics of the haptic devices employed to deliver the force stimulation, and the simplifications introduced in the synthesis algorithms bear significant consequences for the final quality of the haptic experience. When the limits of the device are exceeded or when the algorithm is poorly calibrated, a number of artifacts can corrupt the haptic interaction.;The second component of the thesis is a complete analysis of currently available haptic texture algorithms carried out with a tool called characteristic number. This number summarizes the passivity properties of the synthesis algorithm regardless of their energy profile. This generality required also the introduction of the notion of passive realization of a virtual environment. Both the characteristic number and the concept of passive realization are introduced here for the first time.;The third element of the thesis is a series of two psychophysical experiments aimed at calibrating two texture rendering algorithms with respect to the perceptual strength of the virtual texture stimulus. The method used for the matching has been adapted to the specific needs of haptic rendering, and the results confirm that two algorithms can be calibrated to elicit similar levels of roughness sensation. The passivity margins of two matched algorithms can then be computed and interpreted with the machinery introduced in this thesis.;The redesign of the digital controller of the Pantograph, a haptic device capable of rendering force-feedback haptic textures up to 400 Hz, has been instrumental to the achievements in this work. A novel formulation of a friction based texture algorithm is developed and characterized because it offers advantages over existing approaches.;In this thesis, the problem of generating artifact-free textures is tackled from three different sides. First, a novel framework of six conditions is introduced. These conditions can identify the sources of rendering artifacts related to the hardware properties of the haptic device, and specify the range of textures that can be reliably generated by each haptic device.;In conclusion, this thesis presents a series of innovative tools that can be used to remove the artifacts from the rendering of haptic textures; moreover, a complete rendering platform, device and algorithm, is proposed and evaluated with the novel analysis techniques.