Nail+: sensing fingernail deformation to detect finger force touch interactions on rigid surfaces
A new method for measuring both the posture of human fingers and shear force at human fingertips is presented. Instead of using a traditional electronic glove with bending sensors embedded along the finger and shear sensors embedded beneath the fingertip, a wearable fingernail sensor is used to measure resulting changes in coloration of the fingernail. Since the sensor is mounted on the fingernail, finger posture can be measured without wearing a glove that hampers the motion of the fingers. Similarly, shear forces can be measured without covering the finger pad and obstructing the human’s natural haptic sense. In the past, fingernail sensors with a onedimensional array of photodetectors have been used to measure normal touching forces at the fingertip. A new fingernail sensor with a two-dimensional spatial array of photodetectors is constructed in order to measure finger posture and shear forces. Experiments are performed in order to measure the outputs of the photodetectors in response to changes in finger posture and applied normal and shear forces. Analysis is then performed to correlate the outputs to the inputs and provide a means of estimating normal forces, shear forces, and changes in finger posture.