Seminar Details
2012-05-08 (14.00) : Tactile detection of slip: fine characterization of skin deformation during the onset of slip
At Euler building
Organized by Mathematical Engineering
Speaker :
Delhaye, Benoit
Abstract :
In daily life, we manipulate objects that have different physical properties (mass, surface, shape). Most of the time, we succeed in this task and prevent the objects dropping from the hand. This is explained by the fine coordination between the load force (LF), the tangential force due to the object weight and inertia, and the grip force (GF), the normal force applied to the objects to counteract the LF. This fine coordination is possible with the help of the cutaneous feedback from the fingertips mechanoreceptors. These respond to the stresses and strains created by the deformation of the skin during object grasping and manipulation. Measuring the fingertip skin deformation before and during slipping may thus contribute to better understand how we can prevent the objects from slipping during their manipulation.
In this study, we used an imaging system to record the fingertip deformation during tangential sliding movements of the fingertips on a glass. The constraints were applied passively to the fingertip of subjects in six different directions : front-rear translations, left-right translations and clockwise-counterclockwise rotations. A robotic system controlled the normal force applied to the fingertip and the tangential speed. The contact forces and torques were recorded. Using computer vision techniques, the contact area was extracted from the images and the relative velocity field between the glass and the fingertip contact area was computed during the whole sliding phase. An ellipse was fitted to the contact area during the whole slip in order to measure the displacement (for translations) and the tilt angle (for rotations) of the contact area.
Results showed that the skin deforms in a complex way from a full
stuck state to a full slipping contact. During this transition, while
the tangential force was monotonically increasing, the skin
progressively slipped on the plate, beginning from the border of the
contact area and ending at the central zone, and forming a velocity
gradient from the border to the center. This behavior was observed for
both translational and rotational movements, and was further
characterized...
This is joint work with P. Lefèvre and J-L.Thonnard.