Analysis and modeling of hand-ball contact force during tossing motion

In this study, we observed and analyzed the skillful human motion involved in tossing a ball through a target hole using only wrist and finger motions. In our experiments, two subjects could accomplish this difficult task with skillful finger motion using their wrist, MP, PIP, and DIP joints. Experimental results showed that the ball trajectories from the fingertip of the subjects to the target hole were very similar between the two subjects. Furthermore we analyzed how the subjects controlled the ball motion on their palms so as to match the ball motion with the desired condition to guide the ball to the target hole. In particular, we considered the contact situation between the palm and the ball. However, the contact situation could not be measured or visualized easily, so we constructed a model of the ball motion on the palm, including the effect of the contact forces. After several simulations, we could correctly generate the ball motion and estimate the effect of the contact forces.