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Section: Scientific Foundations

Keywords : tactile device, normal and tangential strain (normal strain, tangential strain).

Tactile actuator

Participants : Melissande Biet, Christophe Chaillou, Frédéric Giraud, François Martinot, Gaston Mboungui, Patricia Plénacoste, Betty Lemaire-Semail, Zheng Dai.

Since several years, research dealing with touch parameters in interaction situation plays an increasing role in the fields of robotics and haptics since fast development in sensors and actuators miniaturizations could allow studying and reproducing touch at small scale. So, one of the main interests in haptics applied to virtual reality is to find a general purpose desktop I/O device that could enhance virtual touch interactions by stimulating the finger pulp.

To achieve that, we first need a better biomechanical knowledge of touching process - and lateral touch more particularly. In the research field, the influence of the friction dynamics used to perceive still remains unclear. First, the action is not sufficiently characterized. Second, there is no existing description of vibratory sources at contact. And finally, frictional and tactile role of fingerprint ridges in roughness estimation is an open research question. Using measurement and signal processing techniques, we analyze the in vivo mechanical behaviour of limbs, pulp and dermatoglyphs of the finger. We look forward finding exploration strategies which will result in new design guidelines for kinaesthetic and tactile displays.

Our team proposes then new technological solutions for fine textures simulation. On the one hand, we are designing high frequency vibratory devices that can output smooth or braking sensation as a function of the amplitude of vibration. Moreover, by using a position sensor, an amplitude modulation of the vibration is achieved in the bandwidth of the mechanoreceptors, so as to excite alternatively shear forces on the surface of the substrate; stimulation is then synchronised on the fingertip's position. This modulation gives rise to simulation of various rippled surface which could be compared with some gratings. On the other hand, in collaboration with the IEMN laboratory (AIMAN) we participate to the study of a dense pin array based either on electromagnetic technology, or pulse air micro-valve technology. Work, based on the guidelines defined above, has to be carried out in order to apply the "good" stimuli on the fingertip so as to improve the sensations. Moreover, we have to take into account ergonomic considerations in the design of devices; for example, we are designing a 2-dof tactile device which enables tactile exploration with a free motion.

Further to touch interactions, force feedback is also needed to reach deeper immersion in virtual environment. Motors used in kinaesthetic devices are often electromagnetic ones, but piezo-electric Ultrasonic Motors are good challengers in these applications because they can be much smaller for the same output torque, or available for multi dof. However their control is not straightforward. This is why we are designing specific control schemes for those motors. Our goal is to build a 3-D haptic device with force feedback, actuated by three Piezo-electric motors. This prototype should depict how much bulk size reduction can be expected.


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