Detection of object contact during grasp using nail-mounted strain sensors

A strain gage glued to the thumbnail was evaluated as a sensor of contact between the thumb and a grasped object. Subjects grasped, lifted, and released a set of standard objects, and the output of the strain gage was amplified in a bridge configuration. The strain signal was high pass filtered, and an amplitude threshold was used to detect contact. Across 3 subjects and 6 objects, contact was detected correctly in 85% of trials. A large number of false positives were also detected, primarily due to object release. This approach has the advantage that it does not interfere with grasp, and these results demonstrate that a nail mounted strain gage can be used to detect object grasp.