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Micromachines
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Soft Actuators: Design, Fabrication and Applications
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Soft Actuators: Design, Fabrication and Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (29 February 2024) | Viewed by 14876

Special Issue Editors

Dr. Chongjing Cao

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Guest Editor
Research Centre for Medical Robotics and Minimally Invasive Surgical Devices, Shenzhen Institute of Advanced Technology (SIAT), Chinese Academy of Sciences, Shenzhen 518055, China
Interests: soft robotics; bioinspired robotics; smart materials; dielectric elastomer actuators; nonlinear dynamics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Bo Li

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Guest Editor
School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Interests: soft robots; smart materials; kirigami; flexible structures
Special Issues, Collections and Topics in MDPI journals
Dr. Xing Gao

E-Mail Website
Guest Editor
Research Centre for Medical Robotics and Minimally Invasive Surgical Devices, Shenzhen Institute of Advanced Technology (SIAT), Chinese Academy of Sciences, Shenzhen 518055, China
Interests: soft robotics; medical robotics; smart materials; dielectric elastomer actuators
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Soft robotics is a fascinating research field that integrates material sciences, robotics and biology to create the next generation of robots that can better adapt to natural environments with complex uncertainties and human-centric operations with strict safety requirements. As one of the core components of soft robots, soft actuators have constantly been the research focus of this particular field. Over the last decade, we have witnessed the rapid development of many novel soft actuators, such as pneu-net and electroactive polymers, which have enabled the agile locomotion and complex task operations of soft robots. However, we need to acknowledge that this field is still faced with a set of key challenges. These include achieving a more efficient/effective actuation of soft actuators through clever and elegant design; developing rapid, yet reliable, fabrication techniques to replace conventional, time-consuming casting for soft actuators; and developing novel applications for these soft actuators that exhibit their true potential in real-world settings.

This Special Issue will be devoted to state-of-the-art research on soft actuators, including the design, fabrication and applications of soft actuators. We seek submissions with original perspectives and advanced thinking on the theme addressed. In particular, the topics of interest include, but are not limited to, the following:

  • Design of soft actuators;
  • Bio-inspired soft actuators;
  • Modeling of soft actuators;
  • Control of soft actuators;
  • Sensing of soft robots;
  • Materials of soft actuators;
  • Advanced fabrication techniques for soft actuators;
  • Artificial intelligence for soft robots;
  • Micro/nano soft actuators;
  • Soft robotic applications.

Dr. Chongjing Cao
Dr. Bo Li
Dr. Xing Gao
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • soft robotics
  • soft actuators
  • smart materials
  • bioinspired designs
  • novel fabrication techniques
  • control of soft actuators
  • soft robotics applications

Related Special Issue

Published Papers (9 papers)

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Research

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13 pages, 2580 KiB  
Article
Simultaneous Measurement of Local Pulse Wave Velocities in Radial Arteries Using a Soft Sensor Based on the Fiber Bragg Grating Technique
by Jing Wang, Zhukun Wang, Zijun Zhang, Peiyun Li, Han Pan, Yong Ren, Tuo Hou, Chengbo Wang, Chiew-Foong Kwong, Bei Zhang, Sen Yang and Jing Bie
Micromachines 2024, 15(4), 507; https://doi.org/10.3390/mi15040507 - 8 Apr 2024
Viewed by 506
Abstract
Arterial stiffness has been proved to be an important parameter in the evaluation of cardiovascular diseases, and Pulse Wave Velocity (PWV) is a strong indicator of arterial stiffness. Compared to regional PWV (PWV among different arteries), local PWV (PWV within a single artery) [...] Read more.
Arterial stiffness has been proved to be an important parameter in the evaluation of cardiovascular diseases, and Pulse Wave Velocity (PWV) is a strong indicator of arterial stiffness. Compared to regional PWV (PWV among different arteries), local PWV (PWV within a single artery) outstands in providing higher precision in indicating arterial properties, as regional PWVs are highly affected by multiple parameters, e.g., variations in blood vessel lengths due to individual differences, and multiple reflection effects on the pulse waveform. However, local PWV is less-developed due to its high dependency on the temporal resolution in synchronized signals with usually low signal-to-noise ratios. This paper presents a method for the noninvasive simultaneous measurement of two local PWVs in both left and right radial arteries based on the Fiber Bragg Grating (FBG) technique via correlation analysis of the pulse pairs at the fossa cubitalis and at the wrist. Based on the measurements of five male volunteers at the ages of 19 to 21 years old, the average left radial PWV ranged from 9.44 m/s to 12.35 m/s and the average right radial PWV ranged from 11.50 m/s to 14.83 m/s. What is worth mentioning is that a stable difference between the left and right radial PWVs was observed for each volunteer, ranging from 2.27 m/s to 3.04 m/s. This method enables the dynamic analysis of local PWVs and analysis of their features among different arteries, which will benefit the diagnosis of early-stage arterial stiffening and may bring more insights into the diagnosis of cardiovascular diseases. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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14 pages, 3289 KiB  
Article
A Current-Mode Analog Front-End for Capacitive Length Transducers in Pneumatic Muscle Actuators
by Guido Di Patrizio Stanchieri, Andrea De Marcellis, Marco Faccio, Elia Palange, Michele Gabrio Antonelli and Pierluigi Beomonte Zobel
Micromachines 2024, 15(3), 377; https://doi.org/10.3390/mi15030377 - 12 Mar 2024
Viewed by 641
Abstract
This paper reports on the design, implementation, and characterization of a current-mode analog-front-end circuit for capacitance-to-voltage conversion that can be used in connection with a large variety of sensors and actuators in industrial and rehabilitation medicine applications. The circuit is composed by: (i) [...] Read more.
This paper reports on the design, implementation, and characterization of a current-mode analog-front-end circuit for capacitance-to-voltage conversion that can be used in connection with a large variety of sensors and actuators in industrial and rehabilitation medicine applications. The circuit is composed by: (i) an oscillator generating a square wave signal whose frequency and pulse width is a function of the value of input capacitance; (ii) a passive low-pass filter that extracts the DC average component of the square wave signal; (iii) a DC-DC amplifier with variable gain ranging from 1 to 1000. The circuit has been designed in the current-mode approach by employing the second-generation current conveyor circuit, and has been implemented by using commercial discrete components as the basic blocks. The circuit allows for gain and sensitivity tunability, offset compensation and regulation, and the capability to manage various ranges of variations of the input capacitance. For a circuit gain of 1000, the measured circuit sensitivity is equal to 167.34 mV/pF with a resolution in terms of capacitance of 5 fF. The implemented circuit has been employed to measure the variations of the capacitance of a McKibben pneumatic muscle associated with the variations of its length that linearly depend on the circuit output voltage. Under step-to-step conditions of movement of the pneumatic muscle, the overall system sensitivity is equal to 70 mV/mm with a standard deviation error of the muscle length variation of 0.008 mm. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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15 pages, 25660 KiB  
Article
Experimental Study on Double-Joint Soft Actuator and Its Dexterous Hand
by Bingxing Chen, Qiuxu Meng, Junjie Wang, Zongxing Lu and Yingjie Cai
Micromachines 2023, 14(10), 1966; https://doi.org/10.3390/mi14101966 - 22 Oct 2023
Viewed by 1071
Abstract
In this paper, we propose a pneumatic double-joint soft actuator based on fiber winding and build a dexterous hand with 11 degrees of freedom. Firstly, soft actuator structural design is carried out according to the actuator driving principle and gives the specific manufacturing [...] Read more.
In this paper, we propose a pneumatic double-joint soft actuator based on fiber winding and build a dexterous hand with 11 degrees of freedom. Firstly, soft actuator structural design is carried out according to the actuator driving principle and gives the specific manufacturing process. Then, an experimental analysis of the bending performance of a single soft actuator, including bending angle, speed, and force magnitude, is carried out by building a pneumatic control experimental platform. Finally, a series of dexterous robotic hand-grasping experiments is conducted. Different grasping methods are used to catch the objects and measure the objects’ change in height, length, and rotation angle during the experiment. The results show that the proposed soft actuator is more consistent with the bending rule of human fingers, and that the gestures of the dexterous hand are more imaginable and flexible when grasping objects. The soft actuator can carry out horizontal and vertical movements, and rotation of the object in the dexterous hand, thus achieving better human–computer interaction. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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18 pages, 7029 KiB  
Article
Design and Additive Manufacturing of a Continuous Servo Pneumatic Actuator
by Gabriel Dämmer, Hartmut Bauer, Michael Lackner, Rüdiger Neumann, Alexander Hildebrandt and Zoltán Major
Micromachines 2023, 14(8), 1622; https://doi.org/10.3390/mi14081622 - 17 Aug 2023
Viewed by 1379
Abstract
Despite an emerging interest in soft and rigid pneumatic lightweight robots, the pneumatic rotary actuators available to date either are unsuitable for servo pneumatic applications or provide a limited angular range. This study describes the functional principle, design, and manufacturing of a servo [...] Read more.
Despite an emerging interest in soft and rigid pneumatic lightweight robots, the pneumatic rotary actuators available to date either are unsuitable for servo pneumatic applications or provide a limited angular range. This study describes the functional principle, design, and manufacturing of a servo pneumatic rotary actuator that is suitable for continuous rotary motion and positioning. It contains nine radially arranged linear bellows actuators with rollers that push forward a cam profile. Proportional valves and a rotary encoder are used to control the bellows pressures in relation to the rotation angle. Introducing freely programmable servo pneumatic commutation increases versatility and allows the number of mechanical components to be reduced in comparison to state-of-the-art designs. The actuator presented is designed to be manufacturable using a combination of standard components, selective laser sintering, elastomer molding with novel multi-part cores and basic tools. Having a diameter of 110 mm and a width of 41 mm, our prototype weighs less than 500 g, produces a torque of 0.53 Nm at 1 bar pressure and a static positioning accuracy of 0.31° with no limit of angular motion. By providing a description of design, basic kinematic equations, manufacturing techniques, and a proof of concept, we enable the reader to envision and explore future applications. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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14 pages, 6531 KiB  
Article
Universally Grasping Objects with Granular—Tendon Finger: Principle and Design
by Van Pho Nguyen, Sunil Bohra Dhyan, Boon Siew Han and Wai Tuck Chow
Micromachines 2023, 14(7), 1471; https://doi.org/10.3390/mi14071471 - 21 Jul 2023
Cited by 3 | Viewed by 1384
Abstract
Nowadays, achieving the stable grasping of objects in robotics requires an increased emphasis on soft interactions. This research introduces a novel gripper design to achieve a more universal object grasping. The key feature of this gripper design was a hybrid mechanism that leveraged [...] Read more.
Nowadays, achieving the stable grasping of objects in robotics requires an increased emphasis on soft interactions. This research introduces a novel gripper design to achieve a more universal object grasping. The key feature of this gripper design was a hybrid mechanism that leveraged the soft structure provided by multiple granular pouches attached to the finger skeletons. To evaluate the performance of the gripper, a series of experiments were conducted using fifteen distinct types of objects, including cylinders, U-shaped brackets, M3 bolts, tape, pyramids, big pyramids, oranges, cakes, coffee sachets, spheres, drink sachets, shelves, pulley gears, aluminium profiles, and flat brackets. Our experimental results demonstrated that our gripper design achieved high success rates in gripping objects weighing less than 210 g. One notable advantage of the granular-tendon gripper was its ability to generate soft interactions during the grasping process while having a skeleton support to provide strength. This characteristic enabled the gripper to adapt effectively to various objects, regardless of their shape and material properties. Consequently, this work presented a promising solution for manipulating a wide range of objects with both stability and soft interaction capabilities, regardless of their individual characteristics. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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15 pages, 10278 KiB  
Article
Hyperelastic Modeling and Validation of Hybrid-Actuated Soft Robot with Pressure-Stiffening
by Majid Roshanfar, Salar Taki, Amir Sayadi, Renzo Cecere, Javad Dargahi and Amir Hooshiar
Micromachines 2023, 14(5), 900; https://doi.org/10.3390/mi14050900 - 22 Apr 2023
Cited by 6 | Viewed by 1827
Abstract
Soft robots have gained popularity, especially in intraluminal applications, because their soft bodies make them safer for surgical interventions than flexures with rigid backbones. This study investigates a pressure-regulating stiffness tendon-driven soft robot and provides a continuum mechanics model for it towards using [...] Read more.
Soft robots have gained popularity, especially in intraluminal applications, because their soft bodies make them safer for surgical interventions than flexures with rigid backbones. This study investigates a pressure-regulating stiffness tendon-driven soft robot and provides a continuum mechanics model for it towards using that in adaptive stiffness applications. To this end, first, a central single-chamber pneumatic and tri-tendon-driven soft robot was designed and fabricated. Afterward, the classic Cosserat’s rod model was adopted and augmented with the hyperelastic material model. The model was then formulated as a boundary-value problem and was solved using the shooting method. To identify the pressure-stiffening effect, a parameter-identification problem was formulated to identify the relationship between the flexural rigidity of the soft robot and internal pressure. The flexural rigidity of the robot at various pressures was optimized to match theoretical deformation and experiments. The theoretical findings of arbitrary pressures were then compared with the experiment for validation. The internal chamber pressure was in the range of 0 to 40 kPa and the tendon tensions were in the range of 0 to 3 N. The theoretical and experimental findings were in fair agreement for tip displacement with a maximum error of 6.40% of the flexure’s length. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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18 pages, 53282 KiB  
Article
A Soft Robot Driven by a Spring-Rolling Dielectric Elastomer Actuator with Two Bristles
by Yangyang Du, Xiaojun Wu, Jiasheng Xue, Xingyu Chen, Chongjing Cao and Xing Gao
Micromachines 2023, 14(3), 618; https://doi.org/10.3390/mi14030618 - 8 Mar 2023
Viewed by 2398
Abstract
Confined space searches such as pipeline inspections are widely demanded in various scenarios, where lightweight soft robots with inherent compliance to adapt to unstructured environments exhibit good potential. We proposed a tubular soft robot with a simple structure of a spring-rolled dielectric elastomer [...] Read more.
Confined space searches such as pipeline inspections are widely demanded in various scenarios, where lightweight soft robots with inherent compliance to adapt to unstructured environments exhibit good potential. We proposed a tubular soft robot with a simple structure of a spring-rolled dielectric elastomer (SRDE) and compliant passive bristles. Due to the compliance of the bristles, the proposed robots can work in pipelines with inner diameters both larger and smaller than the one of the bristles. Firstly, the nonlinear dynamic behaviors of the SRDE were investigated experimentally. Then, we fabricated the proposed robot with a bristle diameter of 19 mm and then studied its performance in pipelines on the ground with inner diameters of 18 mm and 20 mm. When the pipeline’s inner diameter was less than the outer diameter of the bristles, the bristles remained in the state of bending and the robot locomotion is mainly due to anisotropic friction (1.88 and 0.88 body lengths per second horizontally and vertically, respectively, in inner diameter of 18 mm and 0.06 body length per second in that of 16 mm). In the case of the pipeline with the larger inner diameter, the bristles were not fully constrained, and a small bending moment applied on the lower bristle legs contributed to the robot’s locomotion, leading to a high velocity (2.78 body lengths per second in 20 mm diameter acrylic pipe). In addition, the robot can work in varying geometries, such as curving pipes (curve radius ranges from 0.11 m to 0.31 m) at around two body lengths per second horizontally and on the ground at 3.52 body lengths per second, showing promise for pipeline or narrow space inspections. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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Review

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34 pages, 14155 KiB  
Review
Bioinspiration and Biomimetic Art in Robotic Grippers
by Van Pho Nguyen, Sunil Bohra Dhyan, Vu Mai, Boon Siew Han and Wai Tuck Chow
Micromachines 2023, 14(9), 1772; https://doi.org/10.3390/mi14091772 - 15 Sep 2023
Cited by 7 | Viewed by 2917
Abstract
The autonomous manipulation of objects by robotic grippers has made significant strides in enhancing both human daily life and various industries. Within a brief span, a multitude of research endeavours and gripper designs have emerged, drawing inspiration primarily from biological mechanisms. It is [...] Read more.
The autonomous manipulation of objects by robotic grippers has made significant strides in enhancing both human daily life and various industries. Within a brief span, a multitude of research endeavours and gripper designs have emerged, drawing inspiration primarily from biological mechanisms. It is within this context that our study takes centre stage, with the aim of conducting a meticulous review of bioinspired grippers. This exploration involved a nuanced classification framework encompassing a range of parameters, including operating principles, material compositions, actuation methods, design intricacies, fabrication techniques, and the multifaceted applications into which these grippers seamlessly integrate. Our comprehensive investigation unveiled gripper designs that brim with a depth of intricacy, rendering them indispensable across a spectrum of real-world scenarios. These bioinspired grippers with a predominant emphasis on animal-inspired solutions have become pivotal tools that not only mirror nature’s genius but also significantly enrich various domains through their versatility. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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13 pages, 1455 KiB  
Review
Review of Microbottle Resonators for Sensing Applications
by Huda Adnan Zain, Malathy Batumalay, Hazlihan Haris, Ismail Saad, Ahmad Razif Muhammad, Siti Nasuha Mustaffa, Arni Munira Markom, Hazli Rafis Abdul Rahim, Sin Jin Tan and Sulaiman Wadi Harun
Micromachines 2023, 14(4), 734; https://doi.org/10.3390/mi14040734 - 26 Mar 2023
Cited by 1 | Viewed by 1737
Abstract
Microbottle resonators (MBR) are bottle-like structures fabricated by varying the radius of an optical fiber. MBRs can support whispering gallery modes (WGM) by the total internal reflection of the light coupled into the MBRs. MBRs have a significant advantage in sensing and other [...] Read more.
Microbottle resonators (MBR) are bottle-like structures fabricated by varying the radius of an optical fiber. MBRs can support whispering gallery modes (WGM) by the total internal reflection of the light coupled into the MBRs. MBRs have a significant advantage in sensing and other advanced optical applications due to their light confinement abilities in a relatively small mode volume and having high Q factors. This review starts with an introduction to MBRs’ optical properties, coupling methods, and sensing mechanisms. The sensing principle and sensing parameters of MBRs are discussed here as well. Then, practical MBRs fabrication methods and sensing applications are presented. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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