This thesis falls into the field of tactile displays that are meant to produce realistic tactile sensations, which replicate tactile sensations arising naturally when humans interact with the real world. / To begin with we need to know the biomechanics of the glabrous skin in human subjects. To this end, small patches of fingerpad skin are tested in vivo for their biomechanical properties under tangential loading. The skin is quasi-statically stretched and sheared to obtain its effective Young's modulus. Moreover, isotonic and isometric testing conditions are implemented to identify the viscoelasticity model of the skin. The results show a great deal of variability across subjects and it is observed that the glabrous skin exhibits nonlinear stiffening in tangential traction. The skin is consistently more elastic across the ridges, compared to along the ridges, regardless of the location of the sample on the fingerpad. The skin behaves visco-elastically but relaxes about twice as fast as it creeps. Finally, it is found that under large deformation, there is consistently 80% of hysteretic loss for a wide range of loading conditions. / Based on the results obtained by controlled testing, a high performance distributed display is designed. The display has a compact, yet modular structure. Its 6x10 piezo bimorph actuator array has a spatial resolution of 1.8x1.2 millimeters and a wide temporal bandwidth. The actuator mounting method is improved from conventional cantilever to dual-pinned lever, giving the actuator the capability of optimally coupling with glabrous skin. By using previously measured biomechanical data of the skin, we tune the parameters of the actuators to be optimal in terms of real deflection when they couple with the skin. The blocked force of the individual actuators can be adjusted from 0.15 N to 0.22 N to accommodate different applications. It is self-contained in a 150 cm3 volume and may be interfaced to most computers, provided that two analog outputs and six digital IO lines are available. Both public demonstration and psychophysical experiments have validated its effectiveness in rendering virtual tactile features. / The availability of a display raises the question of what signals should be used to drive it in order to render specific sensations. Some progress is made in this direction by analyzing the contact mechanics of fundamental cases, such as isolated indentation and traveling undulation. With the intention of explaining a tactile illusion engendered by straining the fingertip skin tangentially in a progressive wave pattern, resulting in the perception of a moving undulating surface, we carry out a contact mechanics analysis to derive the strain tensor field induced by a sinusoidal surface sliding on a finger, as well as the field created by a tactile transducer array deforming the fingerpad skin by lateral traction. We find that the first field can be well approximated by the second. Our results imply that, first, tactile displays using lateral skin deformation can generate tactile sensations similar to those using normal skin deformation. Second, there is a synthesis approach to achieve this result given constraints on the design of tactile stimulators. Third, the mechanoreceptors embedded in the skin must respond to the deviatoric part of the strain tensor field and not to its volumetric part. Finally, many tactile stimuli might represent for the brain an inverse problem to be solved. / Using the results of these investigations, we have demonstrated the feasibility of producing high-fidelity virtual tactile sensations.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.111874 |
| Date | January 2007 |
| Creators | Wang, Qi, 1971- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Electrical and Computer Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002665524, proquestno: AAINR38661, Theses scanned by UMI/ProQuest. |
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