Experimental investigation of effect of fingertip stiffness on friction while grasping an object

IEEE Robot. Autom. Lett.

Nishimura

Watanabe

2016

Self Cite

Abstract-In this study, we focused on sheet manipulation with robotic hands. This manipulation involves grasping the sides of the sheet and utilizing the convex area resulting from bending the sheet. This sheet manipulation requires the development of a model of a bent sheet grasped with fingertips. We investigated the relationship between the grasping force and bending of the sheet and developed a bent sheet model. We also performed experiments on the sheet grasping stability with a focus on the resistible force, which is defined as the maximum external force at which a fingertip can maintain contact when applying an external force. The main findings and contributions are as follows: 1) After the sheet buckles, the grasping force only increases slightly even if the fingertip pressure is increased.2) The range of the applicable grasping forces depends on the stiffness of the fingertips. Stiffer fingertips cannot provide a small grasping force but can resist large external forces. Softer fingertips can provide a small grasping force but cannot resist large external forces. 3) A grasping strategy for sheet manipulation is presented that is based on controlling the stiffness of the fingertips.

“…15. These results correspond to our previous results, which showed that stiffer fingertips have a higher resistible force (frictional force) [11], [12].…”

Section: B Results and Discussionsupporting

confidence: 81%

“…Watanabe et al [10], [11], [12] investigated the effects of fingertip stiffness on the grasping stability by performing experiments. These studies focused on the contact between rigid objects and soft fingers.…”

Section: A Related Workmentioning

confidence: 99%

Bent Sheet Grasping Stability for Sheet Manipulation

IEEE Robot. Autom. Lett.

Nishimura

Watanabe

2016

Self Cite

“…This made it possible to see the effect of fingertip stiffness more clearly. We also investigated the effect of curvature of the contact surface, which was not investigated in depth in [11]. The main findings are as follows.…”

mentioning

confidence: 99%

“…We include in the definition of this term the effect of fingertip deformation. In contrast to our previous study [11], cylindrical fingertips with flat surfaces were used in this study so that the contact area would remain the same when there was no tangential/shearing force. This made it possible to see the effect of fingertip stiffness more clearly.…”

mentioning

confidence: 99%

Experimental investigation of effect of fingertip stiffness on resistible force in grasping

2015 IEEE International Conference on Robotics and Automation (ICRA)

Harada

Tsuji

et al. 2015

Self Cite

Abstract-In this study, we experimentally investigated the effect of robot fingertip stiffness on the maximum resistible force. The maximum resistible force is defined as the maximum tangential force at which the fingertip can maintain contact when applying and increasing tangential/shearing force. We include in the definition of this term the effect of fingertip deformation. In contrast to our previous study [11], cylindrical fingertips with flat surfaces were used in this study so that the contact area would remain the same when there was no tangential/shearing force. This made it possible to see the effect of fingertip stiffness more clearly. We also investigated the effect of curvature of the contact surface, which was not investigated in depth in [11]. The main findings are as follows. 1) Harder fingertips produce larger resistible forces, irrespective of the shape of the contact surface (flat or curved). 2) For harder fingertips, the maximum resistible force depends largely on the shape of the contact surface, while for softer fingertips, the shape has little effect. 3) For softer fingertips, the magnitude of the resistible force changes little even when the normal force increases.

“…In other words, the pushing distance/force at the danger area starting point is the guaranteed maximum (grasping) force that can avoid fracture. In addition, a phase change from Phase 1 to Phase 2 indicated an alteration in the tofu (it became hard), and there have been reports that a harder contact area can produce larger frictional forces when contacting soft materials [18,19]. Therefore, easier grasping can be expected compared to previous phases.…”

Section: Danger Area Starting Point For Avoiding Fracture and Delmentioning

confidence: 99%

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

Adachi

2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

Watanabe

2015

Self Cite

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.