Softness Effects on Manipulability and Grasp Stability

This paper presents a novel analysis for the effects of softness at the fingertip on the manipulability and stability of grasping. The stability for grasping can be regarded that how much magnitude of external wrench we can balance. We formulate manipulability and the set of generable object wrenches for grasping system, taking deformation of the fingertips into consideration, and show that the increase of the softness decreases the manipulability while it increases generable object wrench. The validity of our analysis is shown by numerical examples. © 2011 IEEE

Development of a Multi-fingered Robot Hand with Softness-changeable Skin Mechanism

This paper develops a multi-fingered robot hand with skin mechanism enabling softness change. We show how the softness of the skin affects grasping and manipulation. Elastic skin provides stable grasping while precise manipulation is lost. Hard skin provides precise manipulation while stability of grasp is lost. We will try to change the softness of the skin according to situation, object, and so on. In this paper, we develop a novel human like robot hand with softnesschangeable skin mechanism

Model-Based Compliance Discrimination via Soft Tactile Optical Sensing and Optical Flow Computation: A Biomimetic Approach

Soft tactile optical sensors have opened up new possibilities for endowing artificial robotic hands with advanced touch-related properties; however, their use for compliance discrimination has been poorly investigated and mainly relies on data-driven methods. Discrimination of object compliance is crucial for enabling accurate and purposeful object manipulation. Humans retrieve this information primarily using the contact area spread rate (CASR) over their fingertips. CASR can be defined as the integral of tactile flow, which describes the movement of iso-strain surfaces within the fingerpad. This work presents the first attempt to discriminate compliance through soft optical tactile sensing based on a computational model of human tactile perception that relies on CASR and tactile flow concepts. To this aim, we used a soft optical biomimetic sensor that transduces surface deformation via movements of marked pins, similar to the function of intermediate ridges in the human fingertip. We acquired images of markers' movements during the interaction with silicone specimens with different compliance at different indenting forces. Then, we computed the optical flow as a tactile flow approximation and its divergence to estimate the CASR. Our model-based approach can accurately discriminate the compliance levels of the specimens, both when the sensor probed the surface perpendicularly and with different inclinations. Finally, we used the relation between specimen compliance and the experimentally evaluated CASR to infer the compliance of a new specimen relying on the estimated CASR

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

In this study, we experimentally investigated the effect of robot fingertip stiffness on friction during grasping of an object. To make robots more human-friendly, robotic hands with soft surfaces have been developed. A soft fingertip, i.e., one with low stiffness, is considered desirable because it produces high friction. However, in our experiments, we were able to obtain high friction from a stiff fingertip under a certain condition. We initially investigated the maximum resistible force when solid objects with different angled surfaces were grasped by spherical fingertips of different stiffness. When the contact surface was flat, a stiffer fingertip produced larger frictional force. When the contact surface was highly convex, the maximum frictional force increased with decreasing fingertip stiffness. Secondly, we examined the relationships among the contact area, the load, and the maximum frictional force. We reformulated the relationship between the load and the maximum frictional force and, together with our experimental results, used it to determine the factor that increased the maximum frictional force. © 2014 IEEE.2014 IEEE International Conference on Robotics and Automation, ICRA 2014; Hong Kong Convention and Exhibition CenterHong Kong; China; 31 May 2014 through 7 June 2014; Category numberCFP14RAA-ART; Code 10739

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

Bent Sheet Grasping Stability for Sheet Manipulation

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

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