Soft Actuators and Robotics

A special issue of Actuators (ISSN 2076-0825). This special issue belongs to the section "Actuators for Robotics".

Deadline for manuscript submissions: closed (1 November 2023) | Viewed by 23903

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Guest Editor
Automation & Robotics Research Group, University of Luxembourg, Luxembourg, Luxembourg
Interests: soft robotics; reconfigurable robotics; robot control; robotic manipulation and grasping
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Special Issue Information

Dear Colleagues,

Relying on their soft bodies, soft actuators and robots are a naturally safe solution to bridge the gap between machines and humans. They can adapt to complex and dynamic environments thanks to their flexibility and compliance. This makes them remarkably advantageous in several applications in developing soft grippers, wearables and haptic devices, artificial muscles, and medical devices.

This Special Issue aims to cover different aspects of the recent advances in soft actuators and robotics, including the development of architectures and modules for fabrication, modeling, sensing, analysis, and control of soft actuators and robotics. Submissions examining how the performance of soft actuators and robotics can be improved and those discussing adaptability, multimodal locomotion, self-healing, and multi-responsiveness of such robots are particularly welcome.

Topics of interest for this collection include but are not limited to:

  • Compliant mechanisms in soft actuators and robotics;
  • Artificial muscles with embedded proprioceptive sensors and electronics;
  • Materials and structural designs of soft actuators;
  • Programmable soft materials in soft actuators and robotics;
  • Modeling and simulation of sensorized actuators;
  • Model-based control of soft actuators and robotics;
  • Data-driven models in soft actuators and robotics;
  • Learning control of soft actuators and robotics;
  • Topology-optimized design in soft actuators and robots;
  • Untethered synthetic soft actuator;
  • Soft actuators in soft grippers;
  • Soft actuators to develop complex soft robots;
  • Real-world applications of soft actuators.

Dr. Hamed Rahimi Nohooji
Guest Editor

Manuscript Submission Information

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Keywords

  • soft robotics
  • soft actuators
  • manufacturing methods in soft robotics
  • topology optimization in soft robotics
  • modeling and control of soft robotics
  • AI in soft robotics
  • soft grippers

Published Papers (10 papers)

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Research

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17 pages, 13662 KiB  
Article
Soft Coiled Pneumatic Actuator with Integrated Length-Sensing Function for Feedback Control
by Jacob R. Greenwood and Wyatt Felt
Actuators 2023, 12(12), 455; https://doi.org/10.3390/act12120455 - 08 Dec 2023
Viewed by 1299
Abstract
SPIRA Coil actuators are formed from thin sheets of PET plastic laminated into a coil shape that unfurls like a “party horn” when inflated, while many soft actuators require large pressures to create only modest strains, SPIRA Coils can easily be designed and [...] Read more.
SPIRA Coil actuators are formed from thin sheets of PET plastic laminated into a coil shape that unfurls like a “party horn” when inflated, while many soft actuators require large pressures to create only modest strains, SPIRA Coils can easily be designed and fabricated to extend over dramatic distances with relatively low working pressures. Internal metalized PET strips separate in the extended portion of the actuator, creating an electrical circuit with a resistance that corresponds to the actuator length. This paper presents and experimentally validates easy-to-use design models for the actuators’ self-retracting spring stiffness, its pneumatic extension force, and its internal length-sensing electrical resistance. Testing of the self-sensing capabilities demonstrates that the embedded sensor can be used to determine the actuator length with virtually no hysteresis. Feedback control with the resistance-based sensing resulted in length-control errors within 5% of the extended actuator length (i.e., 3 cm of 60 cm). Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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15 pages, 4963 KiB  
Article
Octopus-Inspired Robotic Arm Powered by Shape Memory Alloys (SMA)
by Shubham Deshpande and Yara Almubarak
Actuators 2023, 12(10), 377; https://doi.org/10.3390/act12100377 - 04 Oct 2023
Viewed by 1517
Abstract
Traditional rigid grippers that are used for underwater systems lack flexibility and have lower degrees of freedom. These systems might damage the underwater environment while conducting data acquisition and data sampling. Soft robotics, which is mainly focused on creating robots with extremely soft [...] Read more.
Traditional rigid grippers that are used for underwater systems lack flexibility and have lower degrees of freedom. These systems might damage the underwater environment while conducting data acquisition and data sampling. Soft robotics, which is mainly focused on creating robots with extremely soft materials are more delicate for the grasping of objects underwater. These systems tend to damage the underwater ecosystem in the least possible way. In this paper, we have presented a simplified design of a soft arm inspired by the octopus arm actuated by coiled Shape Memory Alloys (SMAs) using completely flexible lightweight material. The characterization arm performance under various load and input current conditions is shown. We hope this work will serve as a basis for the future of underwater grasping utilizing soft robotics. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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21 pages, 8048 KiB  
Article
An Optimized Design of the Soft Bellow Actuator Based on the Box–Behnken Response Surface Design
by Jutamanee Auysakul, Apidet Booranawong, Nitipan Vittayaphadung and Pruittikorn Smithmaitrie
Actuators 2023, 12(7), 300; https://doi.org/10.3390/act12070300 - 24 Jul 2023
Cited by 2 | Viewed by 1492
Abstract
Soft actuator technology is extensively utilized in robotic manipulation applications. However, several existing designs of soft actuators suffer from drawbacks such as a complex casting process, a multi-air chamber configuration, and insufficient grasping force. In this study, we propose a novel soft bellow [...] Read more.
Soft actuator technology is extensively utilized in robotic manipulation applications. However, several existing designs of soft actuators suffer from drawbacks such as a complex casting process, a multi-air chamber configuration, and insufficient grasping force. In this study, we propose a novel soft bellow design featuring a single air chamber, which simplifies the fabrication process of the actual model. To enhance the performance of the proposed design, we employ the Box–Behnken response surface design to generate a design matrix for implementing different levels of design factors in the finite element model. The FEA response is then subjected to an analysis of variance to identify significant factors and establish a regression model for deformation and stress response prediction. Among the considered responses, the wall thickness emerges as the most influential factor, followed by the divided ratio of radians and the number of bellows. Validation of the optimized soft bellow actuator’s deformation response is performed through comparison with experimental data. Moreover, the soft bellow actuator is capable of exerting a pulling force of 8.16 N when used in conjunction with a simple gripper structure design, enabling effective object manipulation. Additionally, the soft bellow design boasts cost-effectiveness and easy moldability, facilitating seamless integration with different gripper frames for diverse applications. Its simplicity and versatility make it a promising choice for various robotic manipulation tasks. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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11 pages, 3441 KiB  
Article
Characteristic Analysis of Heterochiral TCP Muscle as a Extensile Actuator for Soft Robotics Applications
by Beau Ragland and Lianjun Wu
Actuators 2023, 12(5), 189; https://doi.org/10.3390/act12050189 - 28 Apr 2023
Viewed by 1502
Abstract
A soft actuator is an essential component in a soft robot that enables it to perform complex movements by combining different fundamental motion modes. One type of soft actuator that has received significant attention is the twisted and coiled polymer artificial muscle (TCP [...] Read more.
A soft actuator is an essential component in a soft robot that enables it to perform complex movements by combining different fundamental motion modes. One type of soft actuator that has received significant attention is the twisted and coiled polymer artificial muscle (TCP actuator). Despite many recent advancements in TCP actuator research, its use as an extensile actuator is less common in the literature. This works introduces the concept of using TCP actuators as thermal-driven extensile actuators for robotics applications. The low-profile actuator can be easily fabricated to offer two unique deformation capabilities. Results from the characterization indicate that extensile actuators, made with various rod diameters and under different load conditions, display remarkable elongation deformation. Additionally, a proof-of-concept soft-earthworm robot was developed to showcase the potential application of the extensile actuator and to demonstrate the benefits of combining different types of motion modes. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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11 pages, 2807 KiB  
Article
Snakeskin-Inspired 3D Printable Soft Robot Composed of Multi-Modular Vacuum-Powered Actuators
by Seonghyeon Lee, Insun Her, Woojun Jung and Yongha Hwang
Actuators 2023, 12(2), 62; https://doi.org/10.3390/act12020062 - 31 Jan 2023
Cited by 1 | Viewed by 1943
Abstract
A modular soft actuator with snakeskin-inspired scales that generates an anisotropic friction force is designed and evaluated in this study. The actuator makes it possible to fabricate soft robots that can move on various surfaces in the natural environment. For existing modulus soft [...] Read more.
A modular soft actuator with snakeskin-inspired scales that generates an anisotropic friction force is designed and evaluated in this study. The actuator makes it possible to fabricate soft robots that can move on various surfaces in the natural environment. For existing modulus soft robots, additional connectors and several independent pneumatic pumps are required. However, we designed precise connection and snake-scale structures integrated with a single pneumatic modular actuator unit. The precise structure was printed using a DLP 3D printer. The movement characteristics of the soft robot changed according to the angle of the scale structure, and the movement distance increased as the number of modular soft actuator units increased. Soft robots that can move in operating environments such as flat land, tubes, inclined paths, and water have been realized. Furthermore, soft robots with modularization strategies can easily add modular units. We demonstrate the ability to deliver objects 2.5 times heavier than the full weight of the soft robot by adding tong-like structure to the soft robot. The development of a soft robot inspired by snakeskin suggests an easy approach to soft robots that enables various tasks even in environments where existing robots have limited activity. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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15 pages, 8121 KiB  
Article
Handshake Feedback in a Haptic Glove Using Pouch Actuators
by Seiya Yamaguchi, Takefumi Hiraki, Hiroki Ishizuka and Norihisa Miki
Actuators 2023, 12(2), 51; https://doi.org/10.3390/act12020051 - 24 Jan 2023
Cited by 1 | Viewed by 1919
Abstract
In this paper, we propose and demonstrate a haptic device with liquid-pouch motors that can simulate a handshake. Because handshakes involve contact of the palms or soft skin, handshake simulation requires the haptic device to provide pressure onto specific areas of the palm [...] Read more.
In this paper, we propose and demonstrate a haptic device with liquid-pouch motors that can simulate a handshake. Because handshakes involve contact of the palms or soft skin, handshake simulation requires the haptic device to provide pressure onto specific areas of the palm with soft contact. This can be achieved with thermally driven liquid-pouch motors, which inflate and deflate when a low-boiling-point liquid, here Novec™ 7000, evaporates and condenses, respectively. Due to the simplicity of the soft actuator system, this haptic glove is lightweight and conformable. To design the haptic glove, we experimentally investigated the contact region and strength in handshakes, which led to an optimal number, size and position for the liquid-pouch motors. Sensory experiments with human subjects verified that the designed haptic glove successfully simulated handshakes. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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20 pages, 5672 KiB  
Article
An Origami-Inspired Negative Pressure Folding Actuator Coupling Hardness with Softness
by Zhaowen Shao, Wentao Zhao, Zhaotian Zuo, Jun Li and I-Ming Chen
Actuators 2023, 12(1), 35; https://doi.org/10.3390/act12010035 - 10 Jan 2023
Cited by 2 | Viewed by 2311
Abstract
Soft actuators have a high potential for the creative design of flexible robots and safe human–robot interaction. So far, significant progress has been made in soft actuators’ flexibility, deformation amplitude, and variable stiffness. However, there are still deficiencies in output force and force [...] Read more.
Soft actuators have a high potential for the creative design of flexible robots and safe human–robot interaction. So far, significant progress has been made in soft actuators’ flexibility, deformation amplitude, and variable stiffness. However, there are still deficiencies in output force and force retention. This paper presents a new negative pressure-driven folding flexible actuator inspired by origami. First, we establish a theoretical model to predict such an actuator’s output force and displacement under given pressures. Next, five actuators are fabricated using three different materials and evaluated on a test platform. The test results reveal that one actuator generates a maximum pull force of 1125.9 N and the maximum push force of 818.2 N, and another outputs a full force reaching 600 times its weight. Finally, demonstrative experiments are conducted extensively, including stretching, contracting, clamping, single-arm power assistance, and underwater movement. They show our actuators’ performance and feature coupling hardness with softness, e.g., large force output, strong force retention, two-way working, and even muscle-like explosive strength gaining. The existing soft actuators desire these valuable properties. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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16 pages, 5828 KiB  
Article
Design and Test of an Active Pneumatic Soft Wrist for Soft Grippers
by Guangming Chen, Tao Lin, Shi Ding, Shuang Chen, Aihong Ji and Gabriel Lodewijks
Actuators 2022, 11(11), 311; https://doi.org/10.3390/act11110311 - 27 Oct 2022
Cited by 4 | Viewed by 1824
Abstract
An active wrist can deliver both bending and twisting motions that are essential for soft grippers to perform dexterous manipulations capable of producing a wide range movements. Currently, the versions of gripper wrists are relatively heavy due to the bending and twisting motions [...] Read more.
An active wrist can deliver both bending and twisting motions that are essential for soft grippers to perform dexterous manipulations capable of producing a wide range movements. Currently, the versions of gripper wrists are relatively heavy due to the bending and twisting motions performed by the motors. Pneumatic soft actuators can generate multiple motions with lightweight drives. This research evaluates a pneumatic soft wrist based on four parallel soft helical actuators. The kinematics models for predicting bending and twisting motions of this soft wrist are developed. Finite element method simulations are conducted to verify the functions of bending and twisting of this wrist. In addition, the active motions of the soft pneumatic wrist are experimentally demonstrated. Based on sensitivity studies of geometric parameters, a set of parameter values are identified for obtaining maximum bending and twisting angles for a bionic human wrist. Through simulation and experimental tests of the soft wrist for a soft gripper, the desired bending and twisting motions as those of a real human hand wrist are established. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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16 pages, 3866 KiB  
Article
Effects of Flexural Rigidity on Soft Actuators via Adhering to Large Cylinders
by Liuwei Wang, Qijun Jiang, Zhiyuan Weng, Qingsong Yuan and Zhouyi Wang
Actuators 2022, 11(10), 286; https://doi.org/10.3390/act11100286 - 07 Oct 2022
Cited by 3 | Viewed by 1753
Abstract
This study proposes a soft pneumatic actuator with adhesion (SPAA) consisting of a top fluidic-driven elastic actuator and four bottom adhesive pads for adhering to large cylinders. Finite element models were developed to investigate the bending properties under positive air pressure and the [...] Read more.
This study proposes a soft pneumatic actuator with adhesion (SPAA) consisting of a top fluidic-driven elastic actuator and four bottom adhesive pads for adhering to large cylinders. Finite element models were developed to investigate the bending properties under positive air pressure and the effect of “rib” height on the flexural rigidity of the SPAA. A synchronous testing platform for the adhesive contact state and mechanics was developed, and the bending curvature and flexural rigidity of the SPAA were experimentally measured relative to the pressure and “rib” height, respectively, including the adhesion performance of the SPAA with different rigidities on large cylinders. The obtained results indicate that the SPAA can continuously bend with controllable curvature under positive air pressure and can actively envelop a wide range of cylinders of different curvatures. The increase in the “rib” height from 4 to 8 mm increases the flexural rigidity of the SPAA by approximately 230%, contributing to an average increase of 54% in the adhesion performance of the SPAA adhering to large cylinders. The adhesion performance increases more significantly with an increase in the flexural rigidity at a smaller peeling angle. SPAA has a better adhesion performance on large cylinders than most existing soft adhesive actuators, implying that is more stable and less affected by the curvature of cylinders. To address the low contact ratio of the SPAA during adhesion, the optimization designs of the rigid–flexible coupling hierarchical and differentiated AP structures were proposed to increase the contact ratio to more than 80% in the simulation. In conclusion, this study improved the adhesion performance of soft adhesive actuators on large cylinders and extended the application scope of adhesion technology. SPAA is a basic adhesive unit with a universal structure and large aspect ratio similar to that of the human finger. According to working conditions requirements, SPAAs can be assembled to a multi-finger flexible adhesive gripper with excellent maneuverability. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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Review

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25 pages, 5304 KiB  
Review
A Review of Soft Actuator Motion: Actuation, Design, Manufacturing and Applications
by Xianzhi Tang, Huaqiang Li, Teng Ma, Yang Yang, Ji Luo, Haidan Wang and Pei Jiang
Actuators 2022, 11(11), 331; https://doi.org/10.3390/act11110331 - 14 Nov 2022
Cited by 16 | Viewed by 6649
Abstract
Compared with traditional rigid robots, soft robots have high flexibility, low stiffness, and adaptability to unstructured environments, and as such have great application potential in scenarios such as fragile object grasping and human machine interaction. Similar to biological muscles, the soft actuator is [...] Read more.
Compared with traditional rigid robots, soft robots have high flexibility, low stiffness, and adaptability to unstructured environments, and as such have great application potential in scenarios such as fragile object grasping and human machine interaction. Similar to biological muscles, the soft actuator is one of the most important parts in soft robots, and can be activated by fluid, thermal, electricity, magnet, light, humidity, and chemical reaction. In this paper, existing principles and methods for actuation are reviewed. We summarize the preprogrammed and reprogrammed structures under different stimuli to achieve motions such as bending, linear, torsional, spiral. and composite motions, which could provide a guideline for new soft actuator designs. In addition, predominant manufacturing methods and application fields are introduced, and the challenges and future directions of soft actuators are discussed. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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