Identifying 3-D spatiotemporal skin deformation cues evoked in interacting with compliant elastic surfaces
Observing skin deformation over time
August 26, 2020
Bingxu Li, Steven C. Hauser, Gregory J. Gerling
To help us discriminate soft, compliant fruits and tissues, we rely upon tactile cues embedded in the deformation of finger pad skin. Herein, we use a 3-D stereo imaging technique to directly observe patterns in the skin’s deformation. We develop metrics that map 2-D estimates of terminal contact area to 3-D metrics that represent spatial and temporal changes in penetration depth, surface curvature, and force. Human-subjects experiments compare stimulus pairs varying in compliance.
The results indicate that certain metrics more efficiently distinguish compliances earlier, at less displacement. Our observations seek to guide the design and control of haptic actuators.
A custom-built, stereo imaging device is used to obtain 3-D point cloud data for contact of the finger pad with compliant stimuli. The device includes a load cell, a cantilever of a vertically moving indenter, a 3-D printed housing upon which five stimuli can be mounted and rotated in and out of position for vertical indentation, and two cameras for direct stereo visualization with the finger pad beneath. Image processing technique is applied to each frame.
To characterize how the 3-D point cloud changes over the course of an indentation, we developed a method to fit stacked ellipses to discrete, vertically oriented image planes.
We develop new metrics to quantify the patterns of deformation of the skin’s surface as evoked across a range of stimulus compliances, indentation depths, and time scales. In a series of human subjects experiments, a range of stimulus compliances (45 – 184 kPa) are employed, which vary in pairwise discriminability, with rates from 50-100%. the new metrics are compared in effort to determine which might most significantly aid in the discrimination of particular combinations of compliant substrates, considering both discriminability and compliance absolute magnitude.
Li, B., Hauser, S.C., and Gerling, G.J., Identifying 3-D spatiotemporal skin deformation cues evoked in interacting with compliant elastic surfaces [DOI][PDF]. IEEE Haptics Symposium, 2020.
Hauser, S.C. and Gerling, G.J., Imaging the 3-D deformation of the finger pad when interacting with compliant materials [DOI][PDF]. IEEE Haptics Symposium, 2018.
Gregory J. Gerling
Professor, Systems Engineering
151 Engineer's Way Charlottesville, Virginia 22904 Phone: 434-924-0533