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Section: Scientific Foundations

Tactile actuator

Participants : Christophe Chaillou, Frédéric Giraud, Patricia Plénacoste, Betty Lemaire-Semail, Zheng Dai, Mohamad Abdolvahab, Romuald Vanbelleghem.

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.

Today, tactile stimulators based on friction reduction are emerging technologies because they results in lightweight and small devices. They rely on a high frequency vibratory plate 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 synchronized on the fingertip's position. This modulation gives rise to simulation of various rippled surfaces which could be compared with some gratings. Moreover, in order to enlarge the number of types of tactile sensations it's possible to simulate, we colaborate with the IEMN laboratory (AIMAN) to study of a dense pin array based either on electromagnetic technology, or pulse air micro-valve technology.

But feeling has to correspond to the touch of real textures, no matter which technology is used, so we have to apply the "good" stimuli on the fingertip. To achieve such stimulation, we need a better biomechanical knowledge of touching process - and lateral touch more particularly. In this 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 appropriate modelings taking into account those characteristics, we look forward describing physical phenomena located at the contact point between a fingertip and an explored surface in order to deduce the lateral stress field induced by touch movement. At the end, stimuli variation will be found by inverting this modelling.

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. The first prototype should depict how much bulk size reduction can be expected.


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