Measurement of Three-Dimensional Deformation and Load Using Vision-based Tactile Sensor

In this paper, we introduce a tactile sensor which is able to measure the three-dimensional deformation and load simultaneously. The sensor mainly consists of a transparent and elastic body, an 8 x 8 array of markers on the surface of the body and a camera which are used to observe the markers. We present a DFD(Depth from Defocus) algorithm to recover the normal displacement field which has not been solved in previous vision-based tactile sensor. The normal displacement field are combined with shear displacement field to detect the deformation of contact surface and the applied load. Compared to method that calculate normal load only through shear displacement, our method has the advantage of reducing the coupling between normal force and shear force and being able to recover three-dimensional distributed displacement. Experiments are implemented to demonstrate the sensor's performance of measuring shear load, normal load and three-dimensional deformation. The RMSE of measurement of normal displacement is 0.06 mm and the spatial resolution is 1 mm. The sensor can get a real time reconstruction of three-dimensional deformation with a speed of 24fps