New condition for tofu stable grasping with fluid fingertips

Tofu shows the following compression behavior. First, the behavior is non-linear; subsequently, the behavior becomes elastic/linear, followed by yielding and fracture. A linear behavior indicates that there is no fracture, but further increase of compression can cause yielding or fracture. The compression in the region of linear behavior then can be regarded as maximum. With this in mind, this paper presented a grasping condition of controlling the amount of compression so that the compression behavior can be linear. This condition is applied to the previously proposed fluid fingertip that utilizes a rubber bag filled with a viscoelastic fluid and having a rigid layer inside the fluid. In addition, this paper presents a methodology for checking whether the grasping condition is held, based on our previously developed phase change detection method of comparing the fitting accuracies of different approximation models. Additionally, this paper presents the reason behind the behavioral change of fluid pressure. Before phase change, the fluid fingertip behaves like a rigid fingertip, while after phase change, the contact pressure is transmitted to the fluid pressure and can be observed by the fluid pressure. The validity of the approach was shown through experiments.