This paper deals with the problem of force-closure analysis for soft multi-fingered grasps. The first step is the study of the relationship between the external wrench space and the manipulation force space at any con...This paper deals with the problem of force-closure analysis for soft multi-fingered grasps. The first step is the study of the relationship between the external wrench space and the manipulation force space at any contact. Constraint force set, strictly constraint force set and normal force set are defined in the contact force space, followed by an investigation of their relationships. Based on the convexity of the friction constraints for soft finger contact, the necessary and sufficient conditions for force-closure grasps are derived. Accordingly an efficient algorithm for testing force-closure is presented. Some illustrative examples are given.展开更多
A robot slide tactile sensor based on photoelectric devices is introduced.The sensor is mounted on the hydraulic manipulator and used in a soft grasp control system.The experimental results are also presented.
The classical gradient flow optimization algorithm requires a valid initial point before starting the recursive algorithm,and the existing methods can’t guarantee that the initial values fully satisfy the friction co...The classical gradient flow optimization algorithm requires a valid initial point before starting the recursive algorithm,and the existing methods can’t guarantee that the initial values fully satisfy the friction cone constraints of contact point in the optimization process of gradient flow algorithm.In order to improve safety margin and prevent the finger from slipping at contact point,we present an iterative method of safe initial values with safety margin detection and develop a gradient flow optimization algorithm based on the safe initial values.Firstly,the safety margin is defined which more intuitively reflects the margin of the grasping forces at contact point.The resulting safe initial values can be achieved by the detection of desired safety margin at each iteration.Secondly,the safe initial values are usually not optimal,even with the valid initial values,and it can’t always ensure that the finger contact force always satisfies the friction cone constraints during the optimization.It is an effective way to eliminate the unreliable initial values in the optimization and obtain a safer initial values by increasing the safety margin.By transforming the safe initial values into an initial point of the gradient flow algorithm,the final optimized values of grasping forces can be generated efficiently by gradient flow iteration.Grasp examples of the soft multi-fingered hand indicate the effectiveness of the general solution of the force optimization algorithm based on safety margin detection.The method eliminates the shortcomings of the gradient flow optimization process caused by the initial value problem and provides a more accurate and reliable force optimization result for multi-fingered dexterous manipulation.展开更多
提出了一种单顶点多折痕(single-vertex and multi-crease,SVMC)的双稳态折纸软体夹持器,具有结构简单、成本低、变形速度快、承载能力强等优点,有效改善了传统模型响应速度慢、夹持效率低等缺陷。该模型基于水弹结构建立,利用球面三角...提出了一种单顶点多折痕(single-vertex and multi-crease,SVMC)的双稳态折纸软体夹持器,具有结构简单、成本低、变形速度快、承载能力强等优点,有效改善了传统模型响应速度慢、夹持效率低等缺陷。该模型基于水弹结构建立,利用球面三角形余弦定理分析了折痕角度之间的关系并建立运动学方程;同时借助扭簧模型探究变形过程中的势能转化规律。分析了折痕长度与初始角度对能力存储和释放过程的影响,并以此为基础优化了模型结构参数。实验结果表明,当受到2.6 N的外部触发力时,软体夹持器可在61 ms内完成从外展姿态到内缩状态的变化,实现对目标表面的快速包络;同时,借助线绳驱动提供更大的夹紧力,完成对目标的高效稳定抓取。此模型可广泛应用于复杂轮廓目标抓取和快速食品分拣领域。展开更多
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 w...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.展开更多
Soft pneumatic robotic grippers have found extensive applica-tions across various engineering domains,which prompts active research due to their splendid compliance,high flex-ibility,and safe human-robot interaction o...Soft pneumatic robotic grippers have found extensive applica-tions across various engineering domains,which prompts active research due to their splendid compliance,high flex-ibility,and safe human-robot interaction over conventional stiff counterparts.Previously simplified rod-based models prin-cipally focused on clarifying overall large deformation and bending postures of soft grippers from static or quasi-static perspectives,whereas it is challenging to elaborate grasping characteristics of soft grippers without considering contact interaction and nonlinear large deformation behaviors.To address this,based on absolute nodal coordinate formulation(ANCF),comprehensively allowing for structural complexity,geometric,material and boundary nonlinearities,and incorpor-ating Coulomb’friction law with a multiple-point contact method,we put forward an effective nonlinear dynamic mod-eling approach for exploring grasping capability of soft grip-per.Moreover,we solved the established dynamic equations using Generalized-αscheme,and conducted thorough numer-ical simulation analysis on a three-jaw soft pneumatic gripper(SPG)in terms of grasping configurations,displacements and contact forces.The proposed dynamic approach can accurately both describe complicated deformed configurations along with stress distribution and provide a feasible solution to simulate grasping targets,whose effectiveness and precision were analyzed theoretically and verified experimentally,which may shed new light on devising and optimizing other multi-functional SPGs.展开更多
文摘This paper deals with the problem of force-closure analysis for soft multi-fingered grasps. The first step is the study of the relationship between the external wrench space and the manipulation force space at any contact. Constraint force set, strictly constraint force set and normal force set are defined in the contact force space, followed by an investigation of their relationships. Based on the convexity of the friction constraints for soft finger contact, the necessary and sufficient conditions for force-closure grasps are derived. Accordingly an efficient algorithm for testing force-closure is presented. Some illustrative examples are given.
文摘A robot slide tactile sensor based on photoelectric devices is introduced.The sensor is mounted on the hydraulic manipulator and used in a soft grasp control system.The experimental results are also presented.
基金National Natural Science Foundation of China(51305180)International Science&Technology Cooperation Program of China(2014DFR10620)Shandong Provincial Natural Science Foundation(ZR2013FM026,ZR2014YL009)
文摘The classical gradient flow optimization algorithm requires a valid initial point before starting the recursive algorithm,and the existing methods can’t guarantee that the initial values fully satisfy the friction cone constraints of contact point in the optimization process of gradient flow algorithm.In order to improve safety margin and prevent the finger from slipping at contact point,we present an iterative method of safe initial values with safety margin detection and develop a gradient flow optimization algorithm based on the safe initial values.Firstly,the safety margin is defined which more intuitively reflects the margin of the grasping forces at contact point.The resulting safe initial values can be achieved by the detection of desired safety margin at each iteration.Secondly,the safe initial values are usually not optimal,even with the valid initial values,and it can’t always ensure that the finger contact force always satisfies the friction cone constraints during the optimization.It is an effective way to eliminate the unreliable initial values in the optimization and obtain a safer initial values by increasing the safety margin.By transforming the safe initial values into an initial point of the gradient flow algorithm,the final optimized values of grasping forces can be generated efficiently by gradient flow iteration.Grasp examples of the soft multi-fingered hand indicate the effectiveness of the general solution of the force optimization algorithm based on safety margin detection.The method eliminates the shortcomings of the gradient flow optimization process caused by the initial value problem and provides a more accurate and reliable force optimization result for multi-fingered dexterous manipulation.
文摘提出了一种单顶点多折痕(single-vertex and multi-crease,SVMC)的双稳态折纸软体夹持器,具有结构简单、成本低、变形速度快、承载能力强等优点,有效改善了传统模型响应速度慢、夹持效率低等缺陷。该模型基于水弹结构建立,利用球面三角形余弦定理分析了折痕角度之间的关系并建立运动学方程;同时借助扭簧模型探究变形过程中的势能转化规律。分析了折痕长度与初始角度对能力存储和释放过程的影响,并以此为基础优化了模型结构参数。实验结果表明,当受到2.6 N的外部触发力时,软体夹持器可在61 ms内完成从外展姿态到内缩状态的变化,实现对目标表面的快速包络;同时,借助线绳驱动提供更大的夹紧力,完成对目标的高效稳定抓取。此模型可广泛应用于复杂轮廓目标抓取和快速食品分拣领域。
基金funded by the National Natural Science Foundation of China under Grant 62073305 and the Natural Science Foundation of Hubei Province under Grant 2022CFA041.
文摘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.
基金supported by Natural Science Foundation of Zhejiang Province (Grant No.LQ22A020003)National Natural Science Foundation of China (Grant No.52075499)for which all authors are grateful.
文摘Soft pneumatic robotic grippers have found extensive applica-tions across various engineering domains,which prompts active research due to their splendid compliance,high flex-ibility,and safe human-robot interaction over conventional stiff counterparts.Previously simplified rod-based models prin-cipally focused on clarifying overall large deformation and bending postures of soft grippers from static or quasi-static perspectives,whereas it is challenging to elaborate grasping characteristics of soft grippers without considering contact interaction and nonlinear large deformation behaviors.To address this,based on absolute nodal coordinate formulation(ANCF),comprehensively allowing for structural complexity,geometric,material and boundary nonlinearities,and incorpor-ating Coulomb’friction law with a multiple-point contact method,we put forward an effective nonlinear dynamic mod-eling approach for exploring grasping capability of soft grip-per.Moreover,we solved the established dynamic equations using Generalized-αscheme,and conducted thorough numer-ical simulation analysis on a three-jaw soft pneumatic gripper(SPG)in terms of grasping configurations,displacements and contact forces.The proposed dynamic approach can accurately both describe complicated deformed configurations along with stress distribution and provide a feasible solution to simulate grasping targets,whose effectiveness and precision were analyzed theoretically and verified experimentally,which may shed new light on devising and optimizing other multi-functional SPGs.
