Identification of danger state for grasping delicate tofu with fingertips containing viscoelastic fluid

Abstract

Abstract-In this study, we experimentally investigated the process leading to fracture in tofu grasping by deformable fingertips filled with a fluid. In our previous papers [1, 2], we developed deformable fingertips using a rubber bag filled with a viscoelastic fluid, and presented a strategy for delicate tofu grasping without any advance knowledge about fracture. However, the predication point was close to fracture, and the prediction was then still a gamble. In order to realize fracture prediction at an earlier stage, we examined the process leading to fracture when pushing tofu by the deformable fingertips. The stiffness of the fingertips can be controlled with the pressure of the fluid inside the fingertips. The pushing force and fluid pressure were examined for different levels of stiffness of the fingertips. The main findings and contributions are as follows. 1) The convergence of the ratio of the contact force to fluid pressure gives an indication of dent occurrence. This convergence could be seen when fingertip rubber bag was not filled (low stiffness). 2) It was easier for a dent to occur when the fingertip rubber bag was not filled than when it was filled (high stiffness). 3) Changes in the rate of increase of the fluid pressure as the tofu was pushed were repeatedly observed. We defined this as a phase change and present a method for detecting such changes. The phase change points were detected by comparing the fitting accuracies of different approximation models. 4) The last and second to the last phase changes before fracture were detected by detecting the first phase change (after the convergence of the rate of the contact force to fluid pressure if the fingertip bag was not completely filled). The detected points can be regarded as alert points indicating a fracture risk that is not close to the fracture point.

Incompressible liquid based force sensible silicone retractor attachable to surgical suction instruments

“…The diameter of the tubes was so small that the moving distance of water could be captured. Note that this method was valid when the pressure of the magnitude (the stiffness of the sensor part) was equal to or lower than the contact pressure (the stiffness of the target object/tissue), as indicated by previous experimental results [27]. Therefore, the system could have a dead zone where the water does not move even if load was applied to the system.…”

Bent Sheet Grasping Stability for Sheet Manipulation

“…The surface of each fingertip was covered with nitrile rubber to ensure the same friction conditions. The fluid fingertip was the same as the one used for grasping fragile objects in our previous studies [13]. The stiffness of the fluid fingertip can be controlled by adjusting the fluid pressure inside the rubber bag.…”

New condition for tofu stable grasping with fluid fingertips

“…In a human environment, a collision between humans and robots cannot be avoided, and thus, the surfaces of robots should be soft. With this in mind, we previously developed a robotic hand with a soft surface by filling a rubber bag with a viscoelastic fluid, and showed that the hand can grasp a wide variety of fragile objects [1]- [3]. Because of incompressibility, a uniform contact pressure distribution is obtained.…”

“…Y. Fujihira is could not be avoided. We then performed a detailed investigation of the pressure profile, and presented a new method was presented [3]. We showed that tofu could be grasped without fracturing at the point where the behavior of fluid pressure changed.…”

“…This paper also presents a methodology for detecting the elastic behavior of compressed objects. The proposed methodology is based on the phase change detection method [3] of comparing fitting accuracies of different approximation models. Additionally, this paper presents the reason behind the behavioral change of fluid pressure.…”