Bio-Inspired Soft Grippers Based on Impactive Gripping

Abstract

Grasping and manipulation are fundamental ways for many creatures to interact with their environments. Different morphologies and grasping methods of "grippers" are highly evolved to adapt to harsh survival conditions. For example, human hands and bird feet are composed of rigid frames and soft joints. Compared with human hands, some plants like Drosera do not have rigid frames, so they can bend at arbitrary points of the body to capture their prey. Furthermore, many muscular hydrostat animals and plant tendrils can implement more complex twisting motions in 3D space. Recently, inspired by the flexible grasping methods present in nature, increasingly more bio-inspired soft grippers have been fabricated with compliant and soft materials. Based on this, the present review focuses on the recent research progress of bio-inspired soft grippers based on impactive gripping. According to their types of movement and a classification model inspired by biological "grippers", soft grippers are classified into three types, namely, non-continuum bending-type grippers, continuum bending-type grippers, and continuum twisting-type grippers. An exhaustive and updated analysis of each type of gripper is provided. Moreover, this review offers an overview of the different stiffness-controllable strategies developed in recent years.

Keywords: bio‐inspired materials; smart materials; soft actuators; soft grippers; soft robotics; variable stiffness.

Figure 1

The comparison of grippers with the different driving modes, including rigid robotic manipulators (RRM), non‐continuum bending‐type gripper (NBG), continuum bending‐type gripper (CBG), and continuum twisting‐type gripper (CTG) and their typical representatives or counterparts in nature, which include the Gifu Hand II (Reproduced with permission.^{[ 14 ]} Copyright 2012, IEEE), the human hand, the Drosera, and the octopus tentacle. It should be noted that “white components” are regarded as rigid, and “gray components” are regarded as flexible.

Figure 2

Non‐continuum bending‐type grippers (NBGs): A soft gripper with “pouch motors.” Reproduced with permission.^{[ 46 ]} Copyright 2015, Mary Ann Liebert, Inc. A soft micro‐gripper with four fingers. Reproduced with permission.^{[ 47 ]} Copyright 2009, IEEE. A cable‐driven manipulation with elastic finger joints. Reproduced with permission.^{[ 48 ]} Copyright 2017, SAGE Publications. A gripper is driven by a single cable tendon. Reproduced with permission.^{[ 49 ]} Copyright 2015, Mary Ann Liebert, Inc. An omni‐purpose soft gripper incorporated with soft fingers and a suction cup. Reproduced with permission.^{[ 50 ]} Copyright 2019, IEEE. A wireless folding gripper. Reproduced with permission.^{[ 51 ]} Copyright 2017, The American Association for the Advancement of Science. A soft hand with a good bending capacity. Reproduced with permission.^{[ 52 ]} Copyright 2016, Elsevier. A bionic finger is driven by IPMC actuators. Reproduced with permission.^{[ 53 ]} Copyright 2006, IOP Publishing. Continuum bending‐type grippers (CBGs): A flexible pressure‐driven gripper. Reproduced with permission.^{[ 54 ]} Copyright 1990, Cambridge University Press. A soft gripper is used to grasp aquatic mollusk. Reproduced with permission.^{[ 55 ]} Copyright 2019, The American Association for the Advancement of Science. A precharged pneumatic soft gripper. Reproduced with permission.^{[ 56 ]} Copyright 2018, Mary Ann Liebert, Inc. A soft wearable robot for hands. Reproduced with permission.^{[ 57 ]} Copyright 2019, Mary Ann Liebert, Inc. A gripper is driven by SMPs. Reproduced with permission.^{[ 58 ]} Copyright 2015, Springer Nature. Bidirectional SMPs. Reproduced with permission.^{[ 59 ]} Copyright 2013, John Wiley and Sons. An SMA‐based soft gripper. Reproduced with permission.^{[ 60 ]} Copyright 2017, Elsevier. A gripper with SMA springs. Reproduced with permission.^{[ 61 ]} Copyright 2019, IOP Publishing. A soft gripper based on DEME. Reproduced with permission.^{[ 62 ]} Copyright 2007, AIP Publishing. Hydraulically amplified self‐healing electrostatic gripper. Reproduced with permission.^{[ 63 ]} Copyright 2018, The American Association for the Advancement of Science. A microgripper is driven by IPMC. Reproduced with permission.^{[ 101 ]} Copyright 2008, Springer Nature. A Venus flytrap‑inspired microrobot consists of two IPMC actuators. Reproduced with permission.^{[ 65 ]} Copyright 2015, Springer Nature. A micrometer‐scale, light‐driven plier. Reproduced with permission.^{[ 66 ]} Copyright 2020, John Wiley and Sons. Electrically controlled soft gripper with three LCE tubular actuators. Reproduced with permission.^{[ 67 ]} Copyright 2019, The American Association for the Advancement of Science. A polymer electrothermal hand. Reproduced with permission.^{[ 68 ]} Copyright 2015, American Chemical Society. pH‐responsive hydrogel‐based soft micro‐robot. Reproduced with permission.^{[ 69 ]} Copyright 2016, IOP Publishing. Continuum twisting‐type grippers (CTGs): A gripper with multiple bending modes. Reproduced with permission.^{[ 70 ]} Copyright 2012, John Wiley and Sons. A wearable mobile manipulation. Reproduced with permission.^{[ 71 ]} Copyright 2019, Mary Ann Liebert, Inc. A helical soft pressure‐driven actuator. Reproduced with permission.^{[ 72 ]} Copyright 2019, Mary Ann Liebert, Inc. A soft micro‐gripper. Reproduced with permission.^{[ 73 ]} Copyright 2015, Springer Nature. Cable‐driven biomimetic gripper. Reproduced with permission.^{[ 74 ]} Copyright 2012, IOP Publishing. A soft arm inspired by the octopus. Reproduced with permission.^{[ 75 ]} Copyright 2012, Taylor & Francis. A completely soft octopus‐like robotic arm. Reproduced with permission.^{[ 76 ]} Copyright 2012, IEEE. A soft tendril‐inspired twining‐type gripper. Reproduced with permission.^{[ 77 ]} Copyright 2018, American Chemical Society.

Figure 3

The schematic diagrams of SPAs. A) The schematic diagram of CBGs driven by SPAs. B) The schematic diagram of NBGs driven by SPAs. C) The schematic diagram of CTGs driven by SPAs.

Figure 4

NBGs based on SPAs. A) An end‐effector driven by pneumatic balloon actuators. Reproduced with permission.^{[ 130 ]} Copyright 2001, Elsevier. B) A soft micro‐gripper with four fingers.^{[ 47 ]} Reproduced with permission. Copyright 2009, IEEE. C) A soft gripper with “pouch motors.” Reproduced with permission.^{[ 46 ]} Copyright 2015, Mary Ann Liebert, Inc.

Figure 5

CBGs based on SPAs. A) A dexterous robotic hand driven by a PneuFlex actuator. Reproduced with permission.^{[ 140 ]} Copyright 2016, SAGE Publications. B) A bio‐inspired 3D printable soft vacuum gripper. Reproduced with permission.^{[ 141 ]} Copyright 2018, Mary Ann Liebert, Inc. C) A flexible pressure‐driven gripper. Reproduced with permission.^{[ 54 ]} Copyright 1990, Cambridge University Press. D) A starfish‐like gripper. Reproduced with permission.^{[ 108 ]} Copyright 2011, John Wiley and Sons. E) A pressure‐driven gripper with bilaterally curved fingers. Reproduced with permission.^{[ 81 ]} Copyright 2017, Mary Ann Liebert, Inc. F) A gripper with asymmetrical beam structure. Reproduced with permission.^{[ 142 ]} Copyright 2018, National Academy of Sciences – Biactive Work. G) An origami‐inspired gripper. Reproduced with permission.^{[ 143 ]} Copyright 2019, IEEE. H) A modular pressure‐driven actuator. Reproduced with permission.^{[ 144 ]} Copyright 2018, Mary Ann Liebert, Inc. I) A soft gripper fabricated by sculpting. Reproduced with permission.^{[ 82 ]} Copyright 2016, Mary Ann Liebert, Inc. J) A soft gripper used to grasp aquatic mollusk. Reproduced with permission.^{[ 55 ]} Copyright 2019, The American Association for the Advancement of Science. K) A hydraulic gripper based on transparent hydrogel actuators. Reproduced with permission.^{[ 145 ]} Copyright 2017, Springer Nature. L) A self‐healing soft pneumatic gripper. Reproduced with permission.^{[ 146 ]} Copyright 2017, The American Association for the Advancement of Science.

Figure 6

CTGs based on SPAs. A) A 4‐finger gripper. Reproduced with permission.^{[ 169 ]} Copyright 1992, IEEE. B) A gripper with multiple bending modes. Reproduced with permission.^{[ 70 ]} Copyright 2012, John Wiley and Sons. C) OctArm. Reproduced with permission.^{[ 85 ]} Copyright 2006, SPIE. D) A wearable mobile manipulation. Reproduced with permission.^{[ 71 ]} Copyright 2019, Mary Ann Liebert, Inc. E) A helical inflatable gripper. Reproduced with permission.^{[ 172 ]} Copyright 2015, IEEE. F) A helical soft pressure‐driven actuator. Reproduced with permission.^{[ 72 ]} Copyright 2019, Mary Ann Liebert, Inc. G) A high‐load soft gripper. Reproduced with permission.^{[ 79 ]} Copyright 2019, Mary Ann Liebert, Inc. H) A soft micro‐gripper. Reproduced with permission.^{[ 73 ]} Copyright 2015, Springer Nature.

Figure 7

NBGs based on cable‐driven actuators. A) The driving type of the NBGs based on cable‐driven actuators. B) A cable‐driven manipulation with elastic finger joints. Reproduced with permission.^{[ 48 ]} Copyright 2017, SAGE Publications. C) A dexterous tendon‐driven hand. Reproduced with permission.^{[ 195 ]} Copyright 2019. D) A gripper is driven by a single cable tendon. Reproduced with permission.^{[ 49 ]} Copyright 2015, Mary Ann Liebert, Inc. E) An Omni‐purpose soft gripper incorporated with soft fingers and a suction cup. Reproduced with permission.^{[ 50 ]} Copyright 2019, IEEE. F) A biomimetic cable‐driven hand. Reproduced with permission.^{[ 197 ]} Copyright 2016, IEEE. G) An origami‐inspired soft gripper. Reproduced with permission.^{[ 86 ]} Copyright 2019, IEEE.

Figure 8

CBGs, CTGs based on cable‐driven actuators. A) A precharged pneumatic soft gripper. Reproduced with permission.^{[ 56 ]} Copyright 2018, Mary Ann Liebert, Inc. B) A soft wearable robot for hands. Reproduced with permission.^{[ 57 ]} Copyright 2019, Mary Ann Liebert, Inc. C) The schematic diagram of CTGs based on cable‐driven actuators. The dotted lines show the hidden arrangement of the cables and the circle on the right of each picture represents the cross section of the cylinder in which the filled dots represent pulled cables, and empty dots represent released cables. (Modified and redrawn.) Reproduced with permission.^{[ 90 ]} Copyright 2011, Elsevier. D) A cable‐driven biomimetic gripper. Reproduced with permission.^{[ 74 ]} Copyright 2012, IOP Publishing. E) A soft arm inspired by the octopus. Reproduced with permission.^{[ 75 ]} Copyright 2012, Taylor & Francis. F) A variable compliance, soft gripper. Reproduced with permission.^{[ 89 ]} Copyright 2014, Springer Nature.

Figure 9

Soft grippers based on SMAs. A) The shape memory effect of NiTi alloys. (Modified and redrawn.) Reproduced with permission.^{[ 225 ]} Copyright 2018, Springer Nature. B) A wireless folding gripper. Reproduced with permission.^{[ 51 ]} Copyright 2017, The American Association for the Advancement of Science. C) A soft hand with the excellent bending capacity. Reproduced with permission.^{[ 52 ]} Copyright 2016, Elsevier. D) Schematic diagram showing the mechanism of the SMA wire‐based soft actuator. (Modified and redrawn.) Reproduced with permission.^{[ 52 ]} Copyright 2016, Elsevier. E) An SMA‐based soft gripper. Reproduced with permission.^{[ 60 ]} Copyright 2017, Elsevier. F) A gripper with SMA springs. Reproduced with permission.^{[ 61 ]} Copyright 2019, IOP Publishing. G) An anthropomorphic finger actuated by the SMA plate. Reproduced with permission.^{[ 227 ]} Copyright 2015, IOP Publishing. H) A completely soft octopus‐like robotic arm. Reproduced with permission.^{[ 76 ]} Copyright 2012, IEEE.

Figure 10

Soft grippers based on SMPs. A) The process of deforming and recovery of an SMP. (Modified and redrawn.) Reproduced with permission.^{[ 236 ]} Copyright 2002, John Wiley and Sons. B) A gripper is driven by SMPs. Reproduced with permission.^{[ 58 ]} Copyright 2015, Springer Nature. C) A bidirectional gripper based on SMPs. Reproduced with permission.^{[ 59 ]} Copyright 2013, John Wiley and Sons. D) A 3D printed SMP gripper. Reproduced with permission.^{[ 96 ]} Copyright 2016, Springer Nature.

Figure 11

CBGs based on DEAs. A) The working principle of DEAs. (Modified and redrawn.) Reproduced with permission.^{[ 247 ]} Copyright 2018, MDPI AG. B) A soft gripper based on DEME Reproduced with permission.^{[ 62 ]} Copyright 2007, AIP Publishing. C) A responsive DEME soft gripper. Reproduced with permission.^{[ 248 ]} Copyright 2019, Springer Nature. D) A soft gripper with spring‐roll bending actuators. Reproduced with permission.^{[ 249 ]} Copyright 2019, Mary Ann Liebert, Inc. E) A light and flexible DEA gripper. Reproduced with permission.^{[ 250 ]} Copyright 2015, John Wiley and Sons. F) A hydraulic gripper driven by the DEME actuator. Reproduced with permission.^{[ 251 ]} Copyright 2018, IOP Publishing. G) An electrostatic gripper based on hydraulically amplified mechanism. Reproduced with permission.^{[ 63 ]} Copyright 2018, The American Association for the Advancement of Science.

Figure 12

CBGs based on IPMCs. A) The working principle of IPMCs. (Modified and redrawn.) Reproduced with permission.^{[ 268 ]} Copyright 2014, Mary Ann Liebert, Inc. B) A bionic finger driven by IPMC actuators. Reproduced with permission.^{[ 53 ]} Copyright 2006, IOP Publishing. C) A microgripper driven by IPMC. Reproduced with permission.^{[ 101 ]} Copyright 2008,Springer Nature. D) A Venus flytrap‑inspired microrobot consisted of two IPMC actuators. Reproduced with permission.^{[ 65 ]} Copyright 2015, Springer Nature.

Figure 13

CBGS based on LCEs. A) The working principle of LCEs. (Modified and redrawn.) Reproduced with permission.^{[ 262 ]} Copyright 2016, John Wiley and Sons. B) A light‐driven artificial flytrap. Reproduced with permission.^{[ 103 ]} Copyright 2017, Springer Nature. C) A micrometer‐scale, light‐driven plier. Reproduced with permission.^{[ 66 ]} Copyright 2020, John Wiley and Sons. D) An electrically controlled soft gripper with three LCE tubular actuators. Reproduced with permission.^{[ 67 ]} Copyright 2019, The American Association for the Advancement of Science.

Figure 14

Soft grippers based on other smart materials. A) A salt‐responsive bilayer hydrogel. Reproduced with permission.^{[ 296 ]} Copyright 2017, American Chemical Society. B) A mimosa inspired bilayer hydrogel gripper. Reproduced with permission.^{[ 299 ]} Copyright 2018, Royal Society of Chemistry. C) A polymer electrothermal hand. Reproduced with permission.^{[ 68 ]} Copyright 2015, American Chemical Society. D) A light‐sensitive soft finger. Reproduced with permission.^{[ 289 ]} Copyright 2018, John Wiley and Sons. E) A programmable micrometer‐scale robot. Reproduced with permission.^{[ 292 ]} Copyright 2019, The American Association for the Advancement of Science. F) A pH‐responsive hydrogel‐based soft micro‐robot. Reproduced with permission.^{[ 69 ]} Copyright 2016, IOP Publishing. G) A small‐scale soft gripper. Reproduced with permission.^{[ 293 ]} Copyright 2013, Springer Nature. H) A soft gripper responded to humidity. Reproduced with permission.^{[ 294 ]} Copyright 2019, Springer Nature. I) An electrothermal soft gripper. Reproduced with permission.^{[ 290 ]} Copyright 2018, American Chemical Society. J) An insect muscle powered bio‐actuator. Reproduced with permission.^{[ 300 ]} Copyright 2016, Mary Ann Liebert, Inc. K) A soft tendril‐inspired twining‐type gripper. Reproduced with permission.^{[ 77 ]} Copyright 2018, American Chemical Society.

Figure 15

Basic work principles of frequently used jamming objects. A) Granular jamming materials. B) Layered jamming materials. C) Tubular jamming materials.

Figure 16

Soft grippers based on jamming effect. A) A universal jamming gripper. Reproduced with permission.^{[ 311 ]} Copyright 2012, IEEE. B) A two fingers JamHand. Reproduced with permission.^{[ 324 ]} Copyright 2017, Mary Ann Liebert, Inc. C) A ball‐type jamming gripper as a sea sampling tool. Reproduced with permission.^{[ 325 ]} Copyright 2017, Mary Ann Liebert, Inc. D) A variable stiffness robotic gripper by granular jamming. Reproduced with permission.^{[ 326 ]} Copyright 2016, Mary Ann Liebert, Inc. E) A chain‐like granular jamming gripper. Reproduced with permission.^{[ 327 ]} Copyright 2019, Mary Ann Liebert, Inc. F) A soft arm based on tubular stiffening sheath. Reproduced with permission.^{[ 328 ]} Copyright 2018, Mary Ann Liebert, Inc. G) A soft gripper integrated layer jamming units. Reproduced with permission.^{[ 329 ]} Copyright 2019, Mary Ann Liebert, Inc.

Figure 17

Schematic diagrams of ER fluid and MR fluid. A) Basic work principles of ER fluid. (Modified and redrawn.) Reproduced with permission.^{[ 337 ]} Copyright 2019, Royal Society of Chemistry. B) Basic work principles of MR fluid. (Modified and redrawn.) Reproduced with permission.^{[ 338 ]} Copyright 2010, Royal Society of Chemistry.

Figure 18

Stiffness‐controllable soft grippers based on magnetorheological fluids, low‐melting materials, and shape memory materials. A) A universal parallel gripper using MR fluid. Reproduced with permission.^{[ 342 ]} Copyright 2017, IEEE. B) A universal ball‐type robot gripper using MR fluid. Reproduced with permission.^{[ 343 ]} Copyright 2016, World Scientific. C) A pneumatic soft gripper with LMPA stiffness‐controllable structure. Reproduced with permission.^{[ 344 ]} Copyright 2018, IOP Publishing, Ltd. D) A variable stiffness gripper consisted of DEA and LMPA. Reproduced with permission.^{[ 345 ]} Copyright 2015, IEEE. E) A soft gripper with stiffness and shape modulation. Reproduced with permission.^{[ 346 ]} Copyright 2019, Mary Ann Liebert, Inc. F) A three‐fingered pneumatic soft gripper contained ‘‘programmable’’ ligaments. Reproduced with permission.^{[ 347 ]} Copyright 2017, Mary Ann Liebert, Inc. G) An SMA‐based soft gripper with SMP joints. Reproduced with permission.^{[ 348 ]} Copyright 2017, Mary Ann Liebert, Inc. H) A three‐fingered gripper based on SMP variable stiffness module. Reproduced with permission.^{[ 349 ]} Copyright 2019, John Wiley and Sons. I) A soft gripper based on magnetic SMP. Reproduced with permission.^{[ 350 ]} Copyright 2019, John Wiley and Sons.