A Novel Pneumatic Soft Gripper with a Jointed Endoskeleton Structure

In current research on soft grippers,pneumatically actuated soft grippers are generally fabricated using fully soft materials,which have the advantage of flexibility as well as the disadvantages of a small gripping force and slow response speed.To improve these characteristics,a novel pneumatic soft gripper with a jointed endoskeleton structure(E-Gripper)is developed,in which the muscle actuating function has been separated from the force bearing function.The soft action of an E-Gripper finger is performed by some air chambers surrounded by multilayer rubber embedded in the restraining fiber.The gripping force is borne and transferred by the rigid endoskeleton within the E-Gripper finger Thus,the gripping force and action response speed can be increased while the flexibility is maintained.Through experiments,the bending angle of each finger segment,response time,and gripping force of the E-Gripper have been measured,which provides a basis for designing and controlling the soft gripper The test results have shown that the maximum gripping force of the E-Gripper can be 35 N,which is three times greater than that of a fully soft gripper(FS-Gripper)of the same size.At the maximum charging pressure of 150 kPa,the response time is1.123 s faster than that of the FS-Gripper.The research results indicate that the flexibility of a pneumatic soft gripper is not only maintained in the case of the E-Gripper,but its gripping force is also obviously increased,and the response time is reduced.The E-Gripper thus shows great potential for future development and applications.

A Variable Stiffness Soft Gripper Using Granular Jamming and Biologically Inspired Pneumatic Muscles

As the domains, in which robots operate change the objects a robot may be required to grasp and manipulate, are likely to vary sig- nificantly and often. Furthermore there is increasing likelihood that in the future robots will work collaboratively alongside people. There has therefore been interest in the development of biologically inspired robot designs which take inspiration from nature. This paper pre- sents the design and testing of a variable stiffness, three fingered soft gripper, which uses pneumatic muscles to actuate the fingers and granular jamming to vary their stiffness. This gripper is able to adjust its stiffness depending upon how fragile/deformable the object being grasped is. It is also lightweight and low inertia, making it better suited to operation near people. Each finger is formed from a cylindrical rubber bladder filled with a granular material. It is shown how decreasing the pressure inside the finger increases the jamming effect and raises finger stiffness. The paper shows experimentally how the finger stiffness can be increased from 21 N·m^-1 to 71 N·m^-1. The paper also describes the kinematics of the fingers and demonstrates how they can be position-controlled at a range of different stiffness values.

Pneumatic webbed soft gripper for unstructured grasping

Grasping unstructured and fragile objects such as food and fruits is a great challenge for robots.Being naturally different from the traditional rigid robot,soft robotics provide highly promising choices with their intrinsic flexibility and compliance to objects.Inspired by duck foot and octopus tentacle,a pneumatic webbed soft gripper was proposed,which is consisted of four multi-chambered fingers and four webs.Due to its silicone body and soft web structure,the developed soft gripper can naturally adapt,grasp and hold delicate and unstructured objects.Compressed air inflated into the three chambers of the finger actuates the silicone body and performs inflection and extension.The silicone web follows the motion of four fingers,forming a semi-closed grasping configuration.The fingers were fabricated with silicone rubber and constraint spring by casting process.The web was cast around the fingers.The inflecting motion was modeled via the pneumatic principle and geometrical analysis.The dynamic properties of the finger were tested by step and sinusoidal signals.And the grasping performances for different objects,such as egg,strawberry,candy,and knife,were also demonstrated by experiments.The proposed soft gripper performed stably in response to a 0.4 Hz reference sinusoidal signal.The bionic structure greatly improves the stability and reliability of grasping,particularly for unstructured and fragile objects.Moreover,the webs ensure the grasping for multiple objects in one snatch,especially suitable for agricultural products and food processing.

A soft gripper of fast speed and low energy consumption

Grasping of complicated objects is an active research area which is developing fast throughout the years. Soft grippers can be an effective solution, since they are capable of holding workpieces of various shapes and interacting with unstructured environments effectively. Soft grippers generally consist of soft, flexible and compliant materials, which are able to conform to the shape of the object so that the gripper will not deform or bruise the soft object. Fast grasping of objects with various sizes and shapes remains a challenging task for soft grippers. In the present article, a soft gripper based on bi-stable dielectric elastomer actuator(DEA) inspired by the insect-catching ability of the Venus flytrap, is designed. This soft gripper can achieve good performances in grasping various objects by a simple actuation system. The gripper can switch from one stable state to another when subject to an impulse voltage of 0.04 s. The time duration for each grasping action is 0.17 s, and no continuous voltage is required for holding the gripped object. Thus, energy consumption can be achieved as low as 0.1386 J per grasping action. The mechanism of achieving bi-stable states is related to the duration of impulse voltage applied and the resonant frequency of the structure. The present study demonstrates that bi-stable dielectric elastomer actuators are capable of achieving fast speed for grasping with very low energy consumption, which is significant in the applications to soft grippers and biomimetic robots.

高速自适应双稳态折纸软体夹持器设计与分析

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。

折纸形气动软体驱动器设计与性能分析

为了实现气动软体驱动器的大变形,利用折纸结构的折展变形设计一种新型的软体驱动器。建立了该驱动器气压与其弯曲角度之间的关系,建立了驱动器的运动学模型,分析了结构参数对驱动器弯曲性能的影响,分析表明可通过调节气压实现弯曲形态的变化。制作样机,搭建实验平台进行运动和力学性能测试。实验结果表明所设计的驱动器具有两段不同的弯曲特性,可以展现出不同运动形态,可操纵诸如豆腐、水果等表面光滑、易损坏、易变形的物体。当气压为100 kPa时,末端力可达11 N。说明所设计的驱动器具有较好的形状适应性和高负载能力,为软体驱动器设计提供新思路。

轻韧型主动包络软体夹爪设计

为解决传统刚性夹爪刚度大、安全性差以及适用范围受限的问题,课题组提出了一种轻韧型主动包络软体夹爪。夹爪由固定平台和3根软体手爪组成。参考人的手指尺寸和抓取物品时手掌的作用,设计了手爪的尺寸;软体手爪由传统的硅胶沉积浇筑、3D打印等技术加工和制作而成,采用气动驱动方式;基于Yeoh模型对设计的软体手爪的形变进行有限元仿真分析;最后对设计制作的轻韧型主动包络软体手爪进行弯曲和抓取性能测试。实验结果显示:单根软体手爪能够在气压驱动下达到空间内预定的弯曲角度,在60 kPa时手爪达到形变极限位置,指尖接触力为1.12 N。抓取实验结果表明轻韧型主动包络软体夹爪具有良好的包络和承载能力,不仅对规则的刚性物体有好的抓取效果,对不规则物体和质地较为柔软的物品同样有良好的抓持效果。

Soft Robotics:Morphology and Morphology-inspired Motion Strategy

Robotics has aroused huge attention since the 1950s.Irrespective of the uniqueness that industrial applications exhibit,conventional rigid robots have displayed noticeable limitations,particularly in safe cooperation as well as with environmental adaption.Accordingly,scientists have shifted their focus on soft robotics to apply this type of robots more effectively in unstructured environments.For decades,they have been committed to exploring sub-fields of soft robotics(e.g.,cutting-edge techniques in design and fabrication,accurate modeling,as well as advanced control algorithms).Although scientists have made many different efforts,they share the common goal of enhancing applicability.The presented paper aims to brief the progress of soft robotic research for readers interested in this field,and clarify how an appropriate control algorithm can be produced for soft robots with specific morphologies.This paper,instead of enumerating existing modeling or control methods of a certain soft robot prototype,interprets for the relationship between morphology and morphology-dependent motion strategy,attempts to delve into the common issues in a particular class of soft robots,and elucidates a generic solution to enhance their performance.

Bionic soft robotic gripper with feedback control for adaptive grasping and capturing applications

Robots are playing an increasingly important role in engineering applications.Soft robots have promising applications in several fields due to their inherent advantages of compliance,low density,and soft interactions.A soft gripper based on bio-inspiration is proposed in this study.We analyze the cushioning and energy absorption mechanism of human fingertips in detail and provide insights for designing a soft gripper with a variable stiffness structure.We investigate the grasping modes through a large deformation modeling approach,which is verified through experiments.The characteristics of the three grasping modes are quantified through testing and can provide guidance for robotics manipulation.First,the adaptability of the soft gripper is verified by grasping multi-scale and extremely soft objects.Second,a cushioning model of the soft gripper is proposed,and the effectiveness of cushioning is verified by grasping extremely sharp objects and living organisms.Notably,we validate the advantages of the variable stiffness of the soft gripper,and the results show that the soft robot can robustly complete assemblies with a gap of only 0.1 mm.Owing to the unstructured nature of the engineering environment,the soft gripper can be applied in complex environments based on the abovementioned experimental analysis.Finally,we design the soft robotics system with feedback capture based on the inspiration of human catching behavior.The feasibility of engineering applications is initially verified through fast capture experiments on moving objects.The design concept of this robot can provide new insights for bionic machinery.

An effective nonlinear dynamic formulation to analyze grasping capability of soft pneumatic robotic gripper

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.

轻韧型软体夹持器的仿生设计与研究

为了使夹持装置柔软度和承载力兼备,受草本植物茎与花冠结构启发,设计了类似花冠收拢的螺旋式包络和仿植物茎刚度增强方案,每个夹爪呈螺旋状弯曲,通过在夹爪结构内逐个腔室横截面方向嵌入筋板来增大末端输出力,在对变形角度影响较小的条件下有效增大了夹爪末端输出力,并对改善软体执行器的迟滞性有显著效果。制作、组装软体夹爪进行了测试,试验结果表明,轻韧型软体夹持器在自重较轻和收拢尺寸较小的情况下,具备良好展开、包络和承载能力,不仅对轴对称形物体有良好的抓持效果,对于传统夹持器难以夹持的非对称形物体,除花冠式收拢动作外,夹爪还能缠绕物体以增强夹持效果。

机理与数据驱动的软体手弯曲角度软测量模型

由于软体手材料强非线性,难以建立软体手弯曲角度精确的机理模型。针对以上难题,提出机理与数据驱动的软体手弯曲角度软测量模型。该模型由机理模型与信息素挥发及惯性权重的自适应块增量随机配置网络(ABSCN)补偿模型组成。采用最小二乘对机理模型进行参数辨识,针对高阶未建模动态,采用ABSCN预测补偿。通过对块增量随机配置网络(BSC)的增量块配置次数进行自适应优化,提高模型的紧凑性,减少模型的训练时间。最后通过混合模型的仿真实验与真实数据进行对比,结果表明所提方法在精度上有显著提升。

A 0.5-meter-scale,high-load,soft-enclosed gripper capable of grasping the human body

Developing large,soft grippers with high omnidirectional load(above 40 kg)has always been challenging.We address this challenge by developing a powerful soft gripper that can grasp the human body based on a soft-enclosed grasping structure and a soft-rigid coupling structure.The envelope size of the proposed soft gripper is 611.6 mm×559 mm×490.7 mm,the maximum grasping size is 417 mm,and the payload on the human body is more than 90 kg,which has exceeded most existing soft grippers.Furthermore,the grasping force prediction of the gripper is achieved through theoretical modeling.The primary contribution of this work is to overcome the size and payload limits of current soft grippers and implement a human-grasping experiment based on the soft-grasping method.

咽拭子采样软体夹持器结构设计与优化

为了减轻医护人员的工作强度及交叉感染的风险,设计了一种针对咽拭子采样的纯扭转软体夹持器。该夹持器采用螺旋气腔结构并设有安全保护装置。设计了螺旋气腔结构形状和排布方式,基于Abaqus有限元分析软件,并结合正交试验法对气腔结构进行优化设计,选出最优腔型在100 kPa负压时,咽拭子在口腔中划过的弧长为13.88 mm,满足口腔尺寸和采样要求。

Modeling and Experimental Evaluation of a Bionic Soft Pneumatic Gripper with Joint Actuator

The pneumatic gripper in industrial applications has the advantages of structure simplicity and great adaptability,but its gripping power is usually limited due to the low modulus of soft materials.To address this problem,a novel bionic pneumatic gripper inspired by spider legs is proposed.The design has two pairs of symmetrical fingers,each finger consists of two pneumatic actuated joints,two rigid links and one pneumatic soft pad.The rigid link connects the pneumatic chamber which is enclosed in a retractable shell to increase the actuation pressure and the gripping force.The compressibility and elasticity of the soft joint and pad enable the gripper to grasp fragile objects without damage.The modeling of the bionic gripper is developed,and the parameters of the joint actuators are optimized accordingly.The prototype is manufactured and tested with the developed experimental platform,where the gripping force,flexibility and adaptability are evaluated.The results indicate that the designed gripper can grasp irregular and fragile items in sizes from 40 to 140 mm without damage,and the lifting weight is up to 15 N.

无系留气动自适应球果采摘软体手爪设计与实验

为实现球形果实自适应采摘,仿人手触觉传感设计并制作了一种用于球果采摘的无系留智能软体手爪,该手爪采用自循环供气与传感集成,将柔性薄膜触力传感器内嵌于软体手爪内并复合自循环气泵,可实现多尺寸、多类型球果自适应抓取。研究了自循环气泵工作原理,进行了结构优化、压力建模与性能测试。试制了自适应软体手爪原理样机,建立了手爪抓持力模型,并进行了静力学实验,获得了其气压下的弯曲变形和力学特性。建立了球果采摘手爪控制系统与自适应抓取机制,搭建模拟采摘实验平台,进行了自适应抓取实验验证及实验环境下的球果采摘与分拣。结果表明,通过接触力反馈与控制系统,该采摘手爪可安全有效地抓取球果,抓取尺寸范围为48.5~97 mm,最大抓取球果质量为350 g,平均采摘用时15 s,成功率为97.46%。

变刚度柔性夹持装置的研究进展

变刚度柔性夹持装置既保留了软体驱动器的柔顺特性,又有效提高了夹持装置的夹持力。根据结构及驱动方式的不同,变刚度柔性夹持装置主要可分为包含内骨骼或外骨骼结构、基于干扰(阻塞)效应、内嵌低熔点合金或聚合物等3个种类。包含内骨骼或外骨骼结构的夹持装置无法实现刚度的灵活调节;基于干扰效应的夹持装置的两种典型结构中,层干扰比颗粒干扰的刚度调节范围更大,但其结构更复杂,导致制造困难;而内嵌低熔点合金或聚合物的夹持装置,其最大缺陷为响应时间过长,且对设备和驱动器的绝缘以及耐热性能的要求较高。通过分析和总结目前变刚度夹持装置的研究现状,指出目前在该研究领域被忽视的关键问题主要包含3个方面:1)缺少变刚度机理方面的深层次研究;2)缺少变刚度柔性夹持装置可靠性和寿命的研究;3)缺少变刚度柔性夹持装置的应用研究。

一种新型气动肌肉执行器的结构设计与控制研究

传统的气动肌肉执行器存在结构单一、功能低下的问题,为此,基于蛇在蜿蜒运动时的灵感,提出了一种具有向两个相反方向弯曲能力的双弯曲型气动肌肉执行器(DB-PMA)。首先,以传统的收缩式气动肌肉执行器(CPMA)为切入点,描述了DB-PMA的机械结构,包括DB-PMA仿生学设计基础以及DB-PMA的基本机械结构;然后,在“放松”、“加压”、“特殊”3种不同状态下,展开了对DB-PMA的相关运动学分析;并基于DB-PMA进行了实验,对实验结果进行了分析,将其与传统CPMA进行了性能方面的对比;最后,基于该执行器设计了一款软体机械臂,对该机械臂的性能进行了展示,并使用两种方法对其进行了优化改进,并对改进后的机械臂做了分析。研究结果表明:通过第一种改进方法可以使机械臂的最大弯曲角度增加到213°,通过第二种改进方法可以明显地使机械臂的控制更精准;相较于最初的机械臂,两种改进方法均能使机械臂的性能得到了明显的优化与改善。

Design and Grasping Force Modeling for a Soft Robotic Gripper with Multi-stem Twining

To improve the grasping power of soft robots,inspired by the scene of intertwined and interdependent vine branches safely clinging to habitats in a violent storm and the phenomenon of large grasping force after being entangled by aquatic plants,this paper proposes a soft robotic gripper with multi-stem twining.The proposed robotic gripper can realize a larger contact area of surrounding or containing object and more layers of a twining object than the current twining gripping methods.It not only retains the adaptive advantages of twining grasping but also improves the grasping force.First,based on the mechanical characteristics of the multi-stem twining of the gripper,the twining grasping model is developed.Then,the force on the fiber is deduced by using the twining theory,and the axial force of the gripper is analyzed based on the equivalent model of the rubber ring.Finally,the torsion experiments of fibers and the grasping experiments of the gripper are designed and conducted.The torsion experiment of fibers verifies the influence of a different number of fiber ropes and fiber torque on the grasping force,and the grasping experiment reflects the large load of the gripper and the high adaptability and practicability under different tasks.

一种力增强型软体抓取器的设计

随着软体抓取器的研究不断深入,提高其承载能力一直是亟待解决的问题。为此提出一种简单实用的方案,即在软体驱动器的指尖处嵌入磁铁片,通过抓取器指尖之间的磁力增加抓取力。介绍了软体抓取器的结构设计及其制作方法;进行了抓取的力学建模,尤其对指尖贴合时的拉力建模进行了详细分析,得到了理论承载力的大小;对抓取器模型进行了有限元仿真,分析了气压大小与承载力的关系;对理论建模和有限元仿真分析的结果进行对比,二者承载力较无磁铁片嵌入的抓取器分别增加了20.72 N与16.34 N,表明该方案是可行的。该方案为开发出高载荷的软体抓取器提供了新的设计思路。