Comparison of Constrained and Unconstrained Human Grasp Forces Using Fingernail Imaging and Visual Servoing
This work addresses the problem of accurately measuring natural human grasping for robotics and biomechanics, though it is incremental as it builds on prior fingernail imaging methods.
The study compared human grasp forces under constrained and unconstrained conditions using fingernail imaging, finding that unconstrained grasping leads to more evenly distributed forces and less variation among fingers.
Fingernail imaging has been proven to be effective in prior works [1],[2] for estimating the 3D fingertip forces with a maximum RMS estimation error of 7%. In the current research, fingernail imaging is used to perform unconstrained grasp force measurement on multiple fingers to study human grasping. Moreover, two robotic arms with mounted cameras and a visual tracking system have been devised to keep the human fingers in the camera frame during the experiments. Experimental tests have been conducted for six human subjects under both constrained and unconstrained grasping conditions, and the results indicate a significant difference in force collaboration among the fingers between the two grasping conditions. Another interesting result according to the experiments is that in comparison to constrained grasping, unconstrained grasp forces are more evenly distributed over the fingers and there is less force variation (more steadiness) in each finger force. These results validate the importance of measuring grasp forces in an unconstrained manner in order to study how humans naturally grasp objects.