A process of slip between the robot gripper and the object being held was hypothesized. Using multiple modes of contact sensing, experiments were performed to detect evidence that would confirm the hypothesis. Some evidence was found. The experiments, results, and their potential significance are discussed.
"A Search For Precursors Of Slip In Robotic Grasp", Proc. SPIE 0726, Intelligent Robots and Computer Vision V, (27 March 1987); doi: 10.1117/12.937745; https://doi.org/10.1117/12.937745