Enhancing interaction performance of soft pneumatic-networks grippers by skeleton topology optimization

The inherent compliance of soft materials imbues robots,generally referred to as soft robots,with particular advantages in producing adaptive and safe interactions.However,the mainstream design paradigms of soft robots have been focused on pursuing large free motions only,usually at the expense of greatly decreased stiffness,leading to limited capability of withstanding external loads in interactive scenarios.There is a pressing need to incorporate the interaction specifications at the design stage to embody soft robots with not only proper deformability but equally importantly,considerable stiffness to perform complex tasks in practical applications.Here,inspired by the dexterity of human hands,we propose a computational design framework for soft grippers with a focus on improving their interaction performance in power grasping or precision grasping mode.The design paradigm rests on attaching a relatively stiffer skeleton layer to the parametric pneumatic networks based actuator which is widely used due to the geometric advantage,and the skeleton layout is designed for customized interaction conditions by a level set based topology optimization approach.As expected,the optimized skeleton layouts exhibit specified structural features highly relevant to the predefined concentrated loads for precision grip or distributed loads for power grip,which physically implies the compromise between deformability and stiffness.Since the interaction forces are difficult to measure in situ,we devise power and precision grasping scenarios and evaluate the critical actuation pressure of the object’s falling instead.The experiments qualitatively demonstrate the superiority of each specified design.This work represents an initial step toward the rational design for interaction in soft robots.

Soft-rigid coupling grippers:Collaboration strategies and integrated fabrication methods

Continuously increasing applications of robot technologies in unstructured environments put higher requirements on the robotic grippers'performance,such as interaction capability,output force range,and controllability.However,currently,it is hard for either rigid or soft grippers to meet these requirements,as single soft or rigid structures alone are difficult to effectively overcome/alleviate their inherent defects,e.g.,low compliance of rigid structures and low output force of soft structures.To deal with these difficulties,soft-rigid coupling grippers,or hybrid grippers are proposed.Technically,the soft-rigid coupling is a promising design that combines soft and rigid structures,in order to exploit their respective advantages,such as the strength of rigid structures and compliance of soft structures,in the same set of the gripper system.For the first time,herein,this paper systematically discusses the collaboration strategies of the existing hybrid robotic grippers,by classifying them as Rigid-activesoft-passive,Rigid-passive-soft-active,and Rigid-active-soft-active.At the same time,we introduce the integrated fabrication methods of hybrid grippers,through which the soft and rigid structures with great stiffness and property differences can be coupled together to construct a stable system.Also,possible performance improvements on soft-rigid coupling design for gripper systems are discussed.

A Mathematical Modeling Method Elucidating the Integrated Gripping Performance of Ant Mandibles and Bio-inspired Grippers

The ability to grip unhatched eggs is a skill exploited by the ants Harpegnathos venator,as they care their brood in tunneled nests,which is of extreme difficulty to keep the eggs intact while gripping.In this paper we propose a mathematical modeling method to elucidate the mechanism of such a gripping behavior in the ant mandibles.The new method can be subdivided into following steps.As a preliminary,the concavity geometry and mandible kinematics are examined experimentally.Second,coordinate transformation is used to predict the real-time spatial topology of the concavity.Third,we come up with a new method to quantify the workspace required to grip and the contact area between the concavity and ant egg.Our model indicates that the biaxial rotation fashion with specialized concavities can reduce workspace by 40%and increase contact area by 53%on average compared with the uniaxial rotation pattern,which augments success rate of gentle gripping.This methodology may have applications in evaluating mechanical performance in both natural and artificial grippers.

A Track-type Inverted Climbing Robot with Bio-inspired Spiny Grippers

To enable the capacity of climbing robots to work on steep surfaces,especially on inverted surfaces,is a fundamental but challenging task.This capacity can extend the reachable workspace and applications of climbing robots.A track-type inverted climbing robot called SpinyCrawler was developed in this paper.Using a spiny track with an opposed gripping mechanism,the robot was experimentally demonstrated to have the ability of generating considerable adhesion to achieve stable inverted climbing.First,to guarantee reliable attachment of the robot on rough ceilings,a spiny gripper inspired by the opposed gripping prolegs of caterpillars is designed,and a gripping model of the interaction between spines and the ceiling asperities is established and analyzed.Second,a spiny track is developed by assembling dozens of spiny grippers to enable continuous attachment.A cam mechanism is introduced in the robot design without extra actuators to achieve stable attachment and easy detachment during continuous climbing.Finally,climbing experiments are conducted on different surfaces,using a SpinyCrawler prototype.Experimental results demonstrated stable climbing ability on various rough inverted and vertical surfaces,including concrete walls,crushed stone walls,sandpaper walls,brick walls,and brick ceilings.

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.

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.

Review and Prospect of the Shuttleless Loom Development

In this paper, a review of the shuttleless looms’ development shows that three types of shuttleless looms: rapier, Jet and gripper projectile, are now equally matchable with each other. A prospect of the shuttleless loom’s development is also dealt with. It can be predicted that both rapier and Jet looms will be developed further and the future development of a new type of modern weaving looms will be prosperous in the coming 21st century.

Research on vacuumgripper based on fuzzy control for micromanipulators

This paper presents a vacuum gripper （as an actuator of an intelligent micromanipulator） for micro objects （with a diameter of 100 - 300μm） assembly tasks. The gripper is composed of a vacuum unit and a control unit. The vacuum unit with a proportional valve and a pressure sensor, and the control unit with a PC ＋ MCU two-layered control architecture are designed. The mechanical structure, workflow and major programs of the micro-gripper are presented. This paper discusses the major components of the adhesion force acting on micro objects. Some equations of the operation conditions m three phases of pick, hold and place are derived by mechanics analysis. The pneumatic system＇s pressure loss is inevitable. There are some formulas for calculating the amount of the pressure loss, but parameters in formulas are diffficult to be quantified and evaluated. To control the working pressure accurately, a pressure controller based on fuzzy logic is designed. With MATLAB＇s fuzzy logic toolbox, simulation experiments are performed to validate the performance of the fuzzy PD controller. The gripper is characterized by a steady and reliable performance and a simple structure, and it is suitable for handling micro objects with a sub-millimeter size.

A Multi-Scale Grasp Detector Based on Fully Matching Model

Robotic grasping is an essential problem at both the household and industrial levels,and unstructured objects have always been difficult for grippers.Parallel-plate grippers and algorithms,focusing on partial information of objects,are one of the widely used approaches.However,most works predict single-size grasp rectangles for fixed cameras and gripper sizes.In this paper,a multi-scale grasp detector is proposed to predict grasp rectangles with different sizes on RGB-D or RGB images in real-time for hand-eye cameras and various parallel-plate grippers.The detector extracts feature maps of multiple scales and conducts predictions on each scale independently.To guarantee independence between scales and efficiency,fully matching model and background classifier are applied in the network.Based on analysis of the Cornell Grasp Dataset,the fully matching model canmatch all labeled grasp rectangles.Furthermore,background classification,along with angle classification and box regression,functions as hard negative mining and background predictor.The detector is trained and tested on the augmented dataset,which includes images of 320×320 pixels and grasp rectangles ranging from 20 tomore than 320 pixels.It performs up to 98.87% accuracy on image-wise dataset and 97.83% on object-wise split dataset at a speed of more than 22 frames per second.In addition,the detector,which is trained on a single-object dataset,can predict grasps on multiple objects.

Vision-Based Action Control System of a Multi-Finger Mechanical Gripper

A study about the action control of a dexterous mechanical gripper based on stereo-vision system was proposed. The vision-based system was used to replace the data-glove for gesture measurement. The stereo vision theory was applied to calculate the 3D information of the hand gesture. The information was used to generate the grasping action parameters of a 3-finger dexterous mechanical gripper. Combined with a force feedback device, a closed control loop could be constructed. The test for the precision of the algorithms and action control simulation result were shown in the paper.

Design of multisensory integration gripper system for Internet-based teleoperation

A layered architecture of muhisensory integration gripper system is first developed, which includes data acquisition layer, data processing layer and network interface layer. Then we propose a novel support-vector-machine-based data fusion algorithm and also design the gripper system by combining data fusion with CAN bus and CORBA technology, which provides the gripper system with outstanding characteristics such as modularization and intelligence. A multisensory integration gripper test bed is finally built on which a circuit board replacement job based on Internet-based teleoperation is achieved. The experimental results verify the validity of this gripper system design.

Using Microgripper in Development of Automatic Adhesive Glue Transferring and Binding Microassembly System

A system using microgripper for gluing and adhesive bonding in automatic microassembly was designed, implemented, and tested. The development of system is guided by axiomatic design principle. With a compliant PU microgripper, regional-edge-statistics (RES) algorithm, and PD controller, a visual-servoing system was implemented for gripping micro object, gluing adhesive, and operating adhesive bonding. The RES algorithm estimated and tracked a gripper’s centroid to implement a visual-servoing control in the microassembly operation. The main specifications of the system are: gripping range of 60~80μm, working space of 7mm×5.74mm×15mm, system bandwidth of 15Hz. In the performance test, a copper rod with diameter 60μm was automatically gripped and transported for transferring glue and bonding. The 60μm copper rod was dipped into a glue container and moved, pressed and bonding to a copper rod of 380μm. The amount of binding glue was estimated about 5.7nl.

Experimental Results Regarding an Anthropomorphic Original Gripper with Two-Finger Tests during Grasping Objects with Varied Shapes

The paper presents theoretical and experimental results on an original anthropomorphic gripping concept. Compared to the existing anthropomorphic grippers, this gripper is very simple, yet it has the advantage of high performance in terms of gripping possibilities and a very low manufacturing cost. Source of inspiration was the human hand, which is able to catch objects by only using two fingers. The analyzed anthropomorphic gripper has two fingers, with two phalanxes each, and is based on a new mechanism with articulated bars. The kinematic analysis performed on the gripping mechanism reveals the optimal displacement in the translational coupling, which was experimentally validated. The gripping possibilities were increased by attaching clamping jaws to each phalanx. The clamping jaws have been attached by means of spherical couplings, thus offering the possibility to catch objects with any type of surface. By carrying out gripping tests with different objects, we underline the importance of a safe use of the two-fingered anthropomorphic grippers in different applications. Due to the innovative mechanical structure, the gripper can insure the minimal gripping conditions, whilst the complexity of the objects that can be gripped make it suitable for the use in robots.

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.

Detection and removal of excess materials in aircraft wings using continuum robot end-effectors

Excess materials are left inside aircraft wings due to manual operation errors,and the removal of excess materials is very crucial.To increase removal efficiency,a continuum robot(CR)with a removal end-effector and a stereo camera is used to remove excess objects.The size and weight characteristics of excess materials in aircraft wings are analyzed.A novel negative pressure end-effector and a two-finger gripper are designed based on the CR.The negative pressure end-effector aims to remove nuts,small rivets,and small volumes of aluminum shavings.A two-finger gripper is designed to remove large volumes of aluminum shavings.A stereo camera is used to achieve automatic detection and localization of excess materials.Due to poor lighting conditions in the aircraft wing compartment,supplementary lighting devices are used to improve environmental lighting.Then,You Only Look Once(YOLO)v5 is used to classify and detect excess objects,and two training data sets of excess objects in two wings are constructed.Due to the limited texture features inside the aircraft wings,this paper adopts an image-matching method based on the results of YOLO v5 detection.This matching method avoids the performance instability problem based on Oriented Fast and Rotated BRIEF feature point matching.Experimental verification reveals that the detection accuracy of each type of excess exceeds 90%,and the visual localization error is less than 2 mm for four types of excess objects.Results show the two end-effectors can work well for the task of removing excess material from the aircraft wings using a CR.

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.

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.

A Fully Soft Bionic Grasping Device with the Properties of Segmental Bending Shape and Automatically Adjusting Grasping Range

In this paper,we propose a fully Soft Bionic Grasping Device(SBGD),which has advantages in automatically adjusting the grasping range,variable stiffness,and controllable bending shape.This device consists of soft gripper structures and a soft bionic bracket structure.We adopt the local thin-walled design in the soft gripper structures.This design improves the grippers’bending efficiency,and imitate human finger’s segmental bending function.In addition,this work also proposes a pneumatic soft bionic bracket structure,which not only can fix grippers,but also can automatically adjust the grasping space by imitating the human adjacent fingers’opening and closing movements.Due to the above advantages,the SBGD can grasp larger or smaller objects than the regular grasping devices.Particularly,to grasp small objects reliably,we further present a new Pinching Grasping(PG)method.The great performance of the fully SBGD is verified by experiments.This work will promote innovative development of the soft bionic grasping robots,and greatly meet the applications of dexterous grasping multi-size and multi-shape objects.

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.

A Soft Bionic Gripper with Variable Effective Length

This article presented a four-fingered soft bionic robotic gripper with variable effective actuator lengths. By combining approaches of finite element analysis, quasi-static analytical modeling, and experimental measurements, the deformation of the single soft actuator as a function of air pressure input in free space was analyzed. To investigate the effect of the effective actuator length on the gripping per- formance of the gripper, we conducted systematical experiments to evaluate the pull-off force, the actuation speed, the precision and error tolerance of the soft gripper while grasping objects of various sizes and shapes. A combination of depressurization and pressurization in actuation as well as applying variable effective actuator length enhanced the gripper＇s performance significantly, with no sensors. For example, with tunable effective actuator length, the gripper was able to grasp objects ranging from 2 mm 170 mm robustly. Under the optimal length, the gripper could generate the maximum pull-off force for the corresponding object size; the precision and the error tolerance of the gripper were also significantly improved compared to those of the gripper with full-length. Our soft robotic prototype exhibits a simple control and low-cost approach of gripping a wide range of objects and may have wide leverage for future industrial operations.