A Bio-inspired Mutual-hook Strategy for the Soft Finger to Improve Load-bearing Capacity and Grasping Stability

Soft grippers have great potential applications in daily life,since they can compliantly grasp soft and delicate objects.However,the highly elastic fingers of most soft grippers are prone to separate from each other while grasping objects due to their low stiffness,thus reducing the grasping stability and load-bearing capacity.To tackle this problem,inspired from the venus flytrap plant,this work proposes a mutual-hook mechanism to restrain the separation and improve the grasping performance of soft fingers.The novel soft gripper design consists of three modules,a soft finger-cot,two Soft Hook Actuators(SHAs)and two sliding mechanisms.Here,the soft finger-cot covers on the soft finger,increasing the contact area with the target object,two SHAs are fixed to the left and right sides of the finger-cot,and the sliding mechanisms are designed to make SHAs stretch flexibly.Experiments demonstrate that the proposed design can restrain the separation of soft fingers substantially,and the soft fingers with the finger-cots can grasp objects three times heavier than the soft fingers without the proposed design.The proposed design can provide invaluable insights for soft fingers to restrain the separation while grasping,thus improving the grasping stability and the load-bearing capacity.

Tactile-sensing-based robotic grasping stability analysis

Tactile signals play a crucial role in enabling robots to successfully manipulate unfamiliar objects.For robots to grasp unknown objects securely and without causing damage,it is essential that they can analyze grasping stability in real time through tactile signals and respond promptly.This study introduces a novel method for analyzing the stability of robotic hand grasping,utilizing the Wilcoxon signed rank test.The efficacy of this method is demonstrated through its static and dynamic performance,and evaluated across a series of experiments.The findings of this research highlight the method’s ability to accurately detect when an object begins to slip from the robot’s grasp.Employing this method allows the gripper to maintain a secure hold on objects by applying the minimal necessary force.It also enables the gripper to dynamically adjust the force it applies in real time,thus preventing the object from slipping during the movement of the robotic arm.Moreover,the gripper demonstrates the ability to stably grasp objects of varied weights and with unknown characteristics,showcasing the versatility and effectiveness of the proposed method.

Static Stability Analysis of a Single Planar Object Grasped by a.Multifingered Hand

In this study, the static stability of the grasp of a single planar object is analyzed using the potential energy method. In previous papers, we considered cases in which individual fingers were replaced by a multidimensional translational spring model, in which each finger is constructed with prismatic joints. Human hands and the most developed mechanical hands are constructed with revolute joints. In this paper, the effects of fingertip rotation and a revolute joint spring model are investigated. A grasp stiffness matrix is analytically derived by considering not only frictional rolling contact but also frictionless sliding contact. The difl＇erence between the frictional stiffness matrix and the frictionless one is analytically obtained. The effect of local curvature at contact points is analytically derived. The grasp displacement directions affected by the change in curvature and the contact condition are also obtained. The derived stiffness matrix of the revolute joint model is compared with that of the prismatic joint model, and then the stiffness relation is clarified. The gravity effect of the object is also considered. The effectiveness of our method is demonstrated through numerical examples. The stability is evaluated by the eigenvalues of the grasp stiffness matrix, and the grasp displacement direction is obtained by the corresponding eigenvectors. The effect of joint angle is also discussed.

Stability Analysis of Grasps with a Robotic Multifingered Hand

Stability is a significant property for a robot hand grasp to perform complextasks similar to human hands. The common method to investigate the stability of roboticmulti-fingered grasp system is Lyapunov direct method, but usually it is rather difficult toconstruct a proper Lyapunov function. Avoiding the hard work of constructing a Lyapunov function, wepropose the sufficient conditions for stability of the robotic grasp system.