Section: New Results
Simulating fine textured surfaces
Using a stator of Travelling Wave Ultrasonic Motors and a linear position encoder  , we have demonstrated that it is possible to simulate various rippled surfaces with a high frequency vibrating device. Comparison tests with striated layouts etched on a copper printed circuit board have been carried out, and show a good percentage of correct recognition for those specific rough textures  . Then to derive some prerequisite for the design of a new tactile display based on this principle, we suggested carrying out a study to investigate the use of ultrasonic transducer to understand determinants of friction at contact (figure 9 ). Results give the vibration amplitude which is necessary to make a fine textured surface significantly smoother than it is actually. Moreover, we showed that this threshold is larger if the directed movement is done along the epidermal ridges than across  . This suggests that tactile perception of texture really depends on the bearing exerted by the surface state on the skin.