Predicting fingertip forces by imaging coloration changes in the fingernail and surrounding skin

This paper presents an external camera method for measuring fingertip forces by imaging the fingernail and surrounding skin. A 3-D model of the fingernail surface and skin is obtained with a stereo camera and laser striping system. Subsequent images from a single camera are registered to the 3-D model by adding fiducial markings to the fingernail. Calibration results with a force sensor show that the measurement range depends on the region of the fingernail and skin. A generalized least squares model is developed to predict fingertip force given coloration changes, and results for normal and shear force measurement are presented.