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

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. © 2015 IEEE

Visualization Method Based Stiffness Sensing System for Endoscopes

This research developed novel stiffness sensing system attachable to endoscope. The system is an extension of our previous force sensing systems utilizing force visualization mechanism. The sensing part is attached to endoscopes. The force is visualized at the sensing part, and can be measured as visual information via endoscopes. The sensing part also has a structure of limiting the pressing amount. By measuring force at the limitation, the stiffness can be measured. The developed sensing part has the features of no electrical components, disposable, simple, easy sterilization, MRI-compatibility, and low-cost. The validation of the system was experimentally shown. © 2015 IEEE.37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC 2015; MiCo Center, Milano Congressi CenterMilan; Italy; 25 August 2015 through 29 August 2015; Category numberCFP15EMB-ART; Code 11680

Bent sheet grasping stability for sheet manipulation

[email protected] 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. © 2016 IEEE

Identification of Danger State for Grasping Delicate Tofu with Fingertips Containing Viscoelastic Fluid

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. © 2015 IEEE.IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2015; Congress Center Hamburg (CCH)Messeplatz 1Hamburg; Germany; 28 September 2015 through 2 October 2015; Category numberCFP15IRO-ART; Code 11788

Stiffness Measurement System Using Endoscopes with a Visualization Method

A novel stiffness-sensing system was developed that works by attaching the proposed sensing part to endoscopes or cameras. The system provides a method to investigate the stiffness of tissues or objects in deep areas that can only be observed with endoscopes in order to detect abnormalities. The system is an extension of our previous force sensing system that utilized a force visualization mechanism. The force is visualized at the sensing part, and can be measured as visual information via endoscopes or cameras. The sensing part also has a limiting structure used as a threshold for the applied force. By measuring the force at the limitation, the stiffness can be measured. The limitation point is detected by the brightness changes of the captured images. The developed sensing part has the advantages of having no electronic components, being disposable, simple, easy to sterilize, MRI-compatible, and low-cost. Image processing methods for realizing the mechanism are also proposed. The system was experimentally validated. © 2001-2012 IEEE