This paper describes our work on the temporal segmentation of grasping task sequences based on human hand motion. The segmentation process results in the identification of motion breakpoints separating the different constituent phases of the grasping task. A grasping task is composed of three basic phases: pregrasp phase, static grasp phase, and manipulation phase.

We show that by analyzing the fingertip polygon (preshape) area and the speed of hand movement, we can divide a task into meaningful action segments such as approach object, grasp object, manipulate object, place object, and depart. We introduce a measure called the volume sweep rate, which is the product of the fingertip polygon area and the hand speed. The profile of this measure is also used in the determination of the task breakpoints.

The temporal task segmentation process is important as it serves as a preprocessing step to the characterization of the task phases. Once the breakpoints have been identified, further analyses such as grasp recognition and object motion extraction can then be carried out.