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Applied Sciences
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Soft Robotics: New Design, Control, and Application
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Soft Robotics: New Design, Control, and Application

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (31 August 2019) | Viewed by 107812

Special Issue Editor

Prof. Dr. Ki-Uk Kyung

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
Interests: soft sensors and actuators; wearable robots; soft robotics; soft mechatronics; haptics; human–robot interactions
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Soft robotics is a rapidly growing interdisciplinary research area, since deformable features for building robotic and mechatronic systems are expected to have high potential in various applications. Particularly, soft mechanisms may present new opportunities in resolving problems in conventional robotics such as miniaturization, compliant control, wearability, movement on uneven surfaces or in water, and flexibility. This Special Issue welcomes recent advances, challenges, and future perspectives about design, control, and applications in soft robotics. We invite researchers to contribute original works and qualified reviews related to this Special Issue, exploiting recent methodologies for fabricating active soft bodies including compliant sensors and actuators, proposing new approaches in designing soft mechanisms for robotic motions, and addressing challenges in developing dedicated systems for future applications.

Prof. Ki-Uk Kyung
Guest Editor

Manuscript Submission Information

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Keywords

Prospective authors are invited to submit high-quality papers representing results in all areas of soft robotics including, but not limited to, the following:

  • The design of soft robots and their mechanisms
  • Compliant functional materials
  • Soft sensors
  • Soft actuators and artificial muscles
  • Bioinspired mechanism design
  • Control of soft mechanisms
  • Wearable systems and flexible user interfaces
  • Bioinspired grasping, lifting, locomotion, swimming, flying, jumping, and adhesion
  • Manufacturing techniques for soft mechanisms
  • Novel actuation methodology for soft robots
  • Applications of soft robotic and mechatronic systems

Published Papers (19 papers)

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29 pages, 4152 KiB  
Article
A General Approach Based on Newton’s Method and Cyclic Coordinate Descent Method for Solving the Inverse Kinematics
by Yuhan Chen, Xiao Luo, Baoling Han, Yan Jia, Guanhao Liang and Xinda Wang
Appl. Sci. 2019, 9(24), 5461; https://doi.org/10.3390/app9245461 - 12 Dec 2019
Cited by 6 | Viewed by 3116
Abstract
The inverse kinematics of robot manipulators is a crucial problem with respect to automatically controlling robots. In this work, a Newton-improved cyclic coordinate descent (NICCD) method is proposed, which is suitable for robots with revolute or prismatic joints with degrees of freedom of [...] Read more.
The inverse kinematics of robot manipulators is a crucial problem with respect to automatically controlling robots. In this work, a Newton-improved cyclic coordinate descent (NICCD) method is proposed, which is suitable for robots with revolute or prismatic joints with degrees of freedom of any arbitrary number. Firstly, the inverse kinematics problem is transformed into the objective function optimization problem, which is based on the least-squares form of the angle error and the position error expressed by the product-of-exponentials formula. Thereafter, the optimization problem is solved by combining Newton’s method with the improved cyclic coordinate descent (ICCD) method. The difference between the proposed ICCD method and the traditional cyclic coordinate descent method is that consecutive prismatic joints and consecutive parallel revolute joints are treated as a whole in the former for the purposes of optimization. The ICCD algorithm has a convenient iterative formula for these two cases. In order to illustrate the performance of the NICCD method, its simulation results are compared with the well-known Newton–Raphson method using six different robot manipulators. The results suggest that, overall, the NICCD method is effective, accurate, robust, and generalizable. Moreover, it has advantages for the inverse kinematics calculations of continuous trajectories. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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19 pages, 2281 KiB  
Article
Design Methodology for Soft Wearable Devices—The MOSAR Case
by Juana-Mariel Dávila-Vilchis, LAZ-Avilés, Juan Carlos Ávila Vilchis and Adriana H. Vilchis-González
Appl. Sci. 2019, 9(22), 4727; https://doi.org/10.3390/app9224727 - 06 Nov 2019
Cited by 6 | Viewed by 4372
Abstract
This paper proposes a methodology from the conception to the manufacture of soft wearable devices (SWD). This methodology seeks to unify medical, therapeutic and engineering guidelines for research, development and innovation. The aforementioned methodology is divided into two stages (A and B) and [...] Read more.
This paper proposes a methodology from the conception to the manufacture of soft wearable devices (SWD). This methodology seeks to unify medical, therapeutic and engineering guidelines for research, development and innovation. The aforementioned methodology is divided into two stages (A and B) and four phases. Stage A only includes phase 1 to identify the main necessity for a patient that will define the target of its associated device. Stage B encompasses phases 2, 3 and 4. The development of three models (virtual, mathematical and experimental physical) of the required device is addressed in phase 2. Phase 3 concerns the control and manufacture of the experimental physical model (EPM). Phase 4 focuses on the EPM experimental validation. As a result of this methodology, 13 mobility, 11 usability and 3 control iterative design criteria for SWD are reported. Moreover, more than 50 products are provided on a technological platform with modular architectures that facilitate SWD diversification. A case study related to a soft mobilizer for upper limb rehabilitation is reported. Nevertheless, this methodology can be implemented in different areas and accelerates the transition from development to innovation. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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36 pages, 22716 KiB  
Article
Existence Conditions and General Solutions of Closed-form Inverse Kinematics for Revolute Serial Robots
by Wang Shanda, Luo Xiao, Luo Qingsheng and Han Baoling
Appl. Sci. 2019, 9(20), 4365; https://doi.org/10.3390/app9204365 - 16 Oct 2019
Cited by 6 | Viewed by 4263
Abstract
This study proposes a method for judging the existence of closed-form inverse kinematics solutions based on the Denavit–Hartenberg (DH) model. In this method, serial robots with closed-form solutions are described using three types of sub-problems from the viewpoint of solving algebraic equations. If [...] Read more.
This study proposes a method for judging the existence of closed-form inverse kinematics solutions based on the Denavit–Hartenberg (DH) model. In this method, serial robots with closed-form solutions are described using three types of sub-problems from the viewpoint of solving algebraic equations. If a serial robot can be described using these three types of sub-problems, i.e., if the inverse kinematics problems can be solved by several basic problems, then there is a closed-form solution. Based on the above method, we design a set of universal closed-form inverse kinematics solving algorithms. Since there is a definite formula solution for the three types of sub-problems, the joint angles can be rapidly determined. In addition, because the DH parameters can directly reflect the linkage of the robot, the judgment of the sub-problems is also quick and accurate. More importantly, the algorithm can be applied to serial robots with low degrees of freedom. This enables the algorithm to not only quickly and accurately solve inverse kinematics problems but also to exhibit high universality. This proposed theory improves the existence conditions for closed-form reverse solutions and further promotes the development of motion control techniques for serial robots. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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12 pages, 1352 KiB  
Article
Vibration Propagation on the Skin of the Arm
by Valay A. Shah, Maura Casadio, Robert A. Scheidt and Leigh A. Mrotek
Appl. Sci. 2019, 9(20), 4329; https://doi.org/10.3390/app9204329 - 15 Oct 2019
Cited by 13 | Viewed by 3839
Abstract
Vibrotactile interfaces are an inexpensive and non-invasive way to provide performance feedback to body-machine interface users. Interfaces for the upper extremity have utilized a multi-channel approach using an array of vibration motors placed on the upper extremity. However, for successful perception of multi-channel [...] Read more.
Vibrotactile interfaces are an inexpensive and non-invasive way to provide performance feedback to body-machine interface users. Interfaces for the upper extremity have utilized a multi-channel approach using an array of vibration motors placed on the upper extremity. However, for successful perception of multi-channel vibrotactile feedback on the arm, we need to account for vibration propagation across the skin. If two stimuli are delivered within a small distance, mechanical propagation of vibration can lead to inaccurate perception of the distinct vibrotactile stimuli. This study sought to characterize vibration propagation across the hairy skin of the forearm. We characterized vibration propagation by measuring accelerations at various distances from a source vibration of variable intensities (100–240 Hz). Our results showed that acceleration from the source vibration was present at a distance of 4 cm at intensities >150 Hz. At distances greater than 8 cm from the source, accelerations were reduced to values substantially below vibrotactile discrimination thresholds for all vibration intensities. We conclude that in future applications of vibrotactile interfaces, stimulation sites should be separated by a distance of at least 8 cm to avoid potential interference in vibration perception caused by propagating vibrations. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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26 pages, 87486 KiB  
Article
Anthropomorphic Prosthetic Hand with Combination of Light Weight and Diversiform Motions
by Xiaobei Jing, Xu Yong, Yinlai Jiang, Guanglin Li and Hiroshi Yokoi
Appl. Sci. 2019, 9(20), 4203; https://doi.org/10.3390/app9204203 - 09 Oct 2019
Cited by 17 | Viewed by 6031
Abstract
Most prosthetic hands adopt an under-actuated mechanism to achieve dexterous motion performance with a lightweight and anthropomorphic design. Many have been verified in laboratories, and some have already been commercialized. However, a trade-off exists between the dexterity and the light weight of such [...] Read more.
Most prosthetic hands adopt an under-actuated mechanism to achieve dexterous motion performance with a lightweight and anthropomorphic design. Many have been verified in laboratories, and some have already been commercialized. However, a trade-off exists between the dexterity and the light weight of such prosthetic hands. In general, current commercially available prosthetic hands usually consider one aspect at the expense of the other, such as obtaining diversiform hand motions but an increased weight, or achieving lightweight design but with limited motion functions. This study attempts to attain a balance between the two factors, by realizing diversiform hand motions while reducing the weight as far as possible. An anthropomorphic prosthetic hand is proposed with only three servomotors embedded in a human-sized palm, with multiple functions, such as a stable/adaptive grasp and passive hyperextension. The proposed hand can achieve 13 grasp types with over 80% of the grasp motions under the Cutkosky taxonomy, while it weighs only 132.5 g, at less than 36% of the prosthesis weight limitation based on the study of Kay et al. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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15 pages, 4447 KiB  
Article
Design of Shape Memory Alloy-Based Soft Wearable Robot for Assisting Wrist Motion
by Jaeyeon Jeong, Ibrahim Bin Yasir, Jungwoo Han, Cheol Hoon Park, Soo-Kyung Bok and Ki-Uk Kyung
Appl. Sci. 2019, 9(19), 4025; https://doi.org/10.3390/app9194025 - 26 Sep 2019
Cited by 57 | Viewed by 11817
Abstract
In this paper, we propose a shape memory alloy (SMA)-based wearable robot that assists the wrist motion for patients who have difficulties in manipulating the lower arm. Since SMA shows high contraction strain when it is designed as a form of coil spring [...] Read more.
In this paper, we propose a shape memory alloy (SMA)-based wearable robot that assists the wrist motion for patients who have difficulties in manipulating the lower arm. Since SMA shows high contraction strain when it is designed as a form of coil spring shape, the proposed muscle-like actuator was designed after optimizing the spring parameters. The fabricated actuator shows a maximum force of 10 N and a maximum contraction ratio of 40%. The SMA-based wearable robot, named soft wrist assist (SWA), assists 2 degrees of freedom (DOF) wrist motions. In addition, the robot is totally flexible and weighs 151g for the wearable parts. A maximum torque of 1.32 Nm was measured for wrist flexion, and a torque of larger than 0.5 Nm was measured for the other motions. The robot showed the average range of motion (ROM) with 33.8, 30.4, 15.4, and 21.4 degrees for flexion, extension, ulnar, and radial deviation, respectively. Thanks to the soft feature of the SWA, time cost for wearing the device is shorter than 2 min as was also the case for patients when putting it on by themselves. From the experimental results, the SWA is expected to support wrist motion for diverse activities of daily living (ADL) routinely for patients. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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22 pages, 3032 KiB  
Article
Optimal Strokes of Low Reynolds Number Linked-Sphere Swimmers
by Qixuan Wang
Appl. Sci. 2019, 9(19), 4023; https://doi.org/10.3390/app9194023 - 26 Sep 2019
Cited by 11 | Viewed by 2987
Abstract
Optimal gait design is important for micro-organisms and micro-robots that propel themselves in a fluid environment in the absence of external force or torque. The simplest models of shape changes are those that comprise a series of linked-spheres that can change their separation [...] Read more.
Optimal gait design is important for micro-organisms and micro-robots that propel themselves in a fluid environment in the absence of external force or torque. The simplest models of shape changes are those that comprise a series of linked-spheres that can change their separation and/or their sizes. We examine the dynamics of three existing linked-sphere types of modeling swimmers in low Reynolds number Newtonian fluids using asymptotic analysis, and obtain their optimal swimming strokes by solving the Euler–Lagrange equation using the shooting method. The numerical results reveal that (1) with the minimal 2 degrees of freedom in shape deformations, the model swimmer adopting the mixed shape deformation modes strategy is more efficient than those with a single-mode of shape deformation modes, and (2) the swimming efficiency mostly decreases as the number of spheres increases, indicating that more degrees of freedom in shape deformations might not be a good strategy in optimal gait design in low Reynolds number locomotion. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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15 pages, 3479 KiB  
Article
A Low-Cost Soft Robotic Hand Exoskeleton for Use in Therapy of Limited Hand–Motor Function
by Grant Rudd, Liam Daly, Vukica Jovanovic and Filip Cuckov
Appl. Sci. 2019, 9(18), 3751; https://doi.org/10.3390/app9183751 - 08 Sep 2019
Cited by 30 | Viewed by 6374
Abstract
We present the design and validation of a low-cost, customizable and 3D-printed anthropomorphic soft robotic hand exoskeleton for rehabilitation of hand injuries using remotely administered physical therapy regimens. The design builds upon previous work done on cable actuated exoskeleton designs by implementing the [...] Read more.
We present the design and validation of a low-cost, customizable and 3D-printed anthropomorphic soft robotic hand exoskeleton for rehabilitation of hand injuries using remotely administered physical therapy regimens. The design builds upon previous work done on cable actuated exoskeleton designs by implementing the same kinematic functionality, but with the focus shifted to ease of assembly and cost effectiveness as to allow patients and physicians to manufacture and assemble the hardware necessary to implement treatment. The exoskeleton was constructed solely from 3D-printed and widely available off-the-shelf components. Control of the actuators was realized using an Arduino microcontroller, with a custom-designed shield to facilitate ease of wiring. Tests were conducted to verify that the range of motion of the digits and the forces exerted at the fingertip coincided with those of a healthy human hand. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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17 pages, 6484 KiB  
Article
A Snake-Like Robot with Envelope Wheels and Obstacle-Aided Gaits
by Kundong Wang, Youwei Ma, Haoxuan Shan and Shugen Ma
Appl. Sci. 2019, 9(18), 3749; https://doi.org/10.3390/app9183749 - 08 Sep 2019
Cited by 5 | Viewed by 4225
Abstract
Most of the current snake-like robots can only work in a specific environment, or only have a good movement effect in a certain gait. This paper presents a design for a snake-like robot to improve the adaptability of various environments. Each standard module [...] Read more.
Most of the current snake-like robots can only work in a specific environment, or only have a good movement effect in a certain gait. This paper presents a design for a snake-like robot to improve the adaptability of various environments. Each standard module of the snake-like robot has three degrees of freedom: yawing, rolling, and telescoping. The envelope passive wheels are used to enable the robot to move in complex environments such as a narrow passage. We verified some simple movements such as serpentine movement and rectilinear movement and designed a method for recovering from rollover when the robot is in straight state. In addition, two novel gaits, obstacle-aided concertina gait, and obstacle-aided gait through narrow corner, are proposed in this paper. We demonstrated the feasibility for passing the narrow corner by these gaits in experiments. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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16 pages, 7645 KiB  
Article
Soft Robotic Gripper with Chambered Fingers for Performing In-Hand Manipulation
by Khulan Batsuren and Dongwon Yun
Appl. Sci. 2019, 9(15), 2967; https://doi.org/10.3390/app9152967 - 24 Jul 2019
Cited by 27 | Viewed by 5681
Abstract
In this work, we present a soft robotic gripper for grasping various objects by mimicking in-hand manipulation. The soft robotic gripper consists of three fingers. Each finger contains three air chambers: Two chambers (side chambers) for twisting in two different directions and one [...] Read more.
In this work, we present a soft robotic gripper for grasping various objects by mimicking in-hand manipulation. The soft robotic gripper consists of three fingers. Each finger contains three air chambers: Two chambers (side chambers) for twisting in two different directions and one chamber (middle chamber) for grasping. The combination of these air chambers makes it possible to grasp an object and rotate it. We fabricated the soft finger using 3D-printed molds. We used the finite element method (FEM) method to design the most effective model, and later these results were compared with results from experiments. The combined experimental results were used to control the range of movement of the whole gripper. The gripper could grasp objects weighing from 4 g to 300 g just by inflating the middle chamber, and when air pressure was subsequently applied to one of the side chambers, the gripper could twist the object by 35°. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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15 pages, 1825 KiB  
Article
Form-Finding Analysis of a Class 2 Tensegrity Robot
by Carlos G. Manríquez-Padilla, Oscar A. Zavala-Pérez, Gerardo I. Pérez-Soto, Juvenal Rodríguez-Reséndiz and Karla A. Camarillo-Gómez
Appl. Sci. 2019, 9(15), 2948; https://doi.org/10.3390/app9152948 - 24 Jul 2019
Cited by 5 | Viewed by 3636
Abstract
In this paper, a new form-finding analysis methodology for a class 2 tensegrity robot is proposed. The methodology consists of two steps: first, the analysis of the possible geometric configurations of the robot is carried out through the results of the kinematic position [...] Read more.
In this paper, a new form-finding analysis methodology for a class 2 tensegrity robot is proposed. The methodology consists of two steps: first, the analysis of the possible geometric configurations of the robot is carried out through the results of the kinematic position analysis; and, second, from the static analysis, the equilibrium positions of the robot are found, which represents its workspace. Both kinematics and static analysis are resolved in a closed-form using basic tools of linear algebra instead of the strategies used in literature. Four numerical experiments are presented using the finite element analysis software ANSYS©. Additionally, a comparison between the results of the form-finding analysis methodology proposed and the ANSYS© results is presented. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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10 pages, 261 KiB  
Article
Stroke Gait Rehabilitation: A Comparison of End-Effector, Overground Exoskeleton, and Conventional Gait Training
by Michela Goffredo, Chiara Iacovelli, Emanuele Russo, Sanaz Pournajaf, Chiara Di Blasi, Daniele Galafate, Leonardo Pellicciari, Maurizio Agosti, Serena Filoni, Irene Aprile and Marco Franceschini
Appl. Sci. 2019, 9(13), 2627; https://doi.org/10.3390/app9132627 - 28 Jun 2019
Cited by 28 | Viewed by 5262
Abstract
Gait recovery is one of the main goals of post-stroke rehabilitation and Robot-Assisted Gait Training (RAGT) has shown positive outcomes. However, there is a lack of studies in the literature comparing the effects of different devices. This paper aims to study the effects, [...] Read more.
Gait recovery is one of the main goals of post-stroke rehabilitation and Robot-Assisted Gait Training (RAGT) has shown positive outcomes. However, there is a lack of studies in the literature comparing the effects of different devices. This paper aims to study the effects, in terms of clinical and gait outcomes, of treadmill-based and overground RAGT, compared to conventional gait training in stroke subjects. The results showed a significant improvement of clinical outcomes in both robotic treatments and in conventional therapy. The performance of locomotor tasks was clinically significant in the robotic groups only. The spatio-temporal gait parameters did not reveal any significant difference. Results suggest future multicentre studies on a larger number of subjects. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
17 pages, 3914 KiB  
Article
Dynamic Modeling of McKibben Muscle Using Empirical Model and Particle Swarm Optimization Method
by Mohd Azuwan Mat Dzahir and Shin-ichiroh Yamamoto
Appl. Sci. 2019, 9(12), 2538; https://doi.org/10.3390/app9122538 - 21 Jun 2019
Cited by 6 | Viewed by 4859
Abstract
This paper explores empirical modeling of McKibben muscle in characterizing its hysteresis behavior and nonlinearities during quasi-static, quasi-rate, and historic dependencies. The unconventional materials-based actuating system called McKibben muscle has excellent properties of power-to-weight ratio, which could be used in rehabilitation orthosis application [...] Read more.
This paper explores empirical modeling of McKibben muscle in characterizing its hysteresis behavior and nonlinearities during quasi-static, quasi-rate, and historic dependencies. The unconventional materials-based actuating system called McKibben muscle has excellent properties of power-to-weight ratio, which could be used in rehabilitation orthosis application for condition monitoring, physical enhancement, and rehabilitation therapy. McKibben muscle is known to exhibit hysteresis behavior and it is rate-dependent (the level of hysteresis depends closely on rate of input excitation frequency). This behavior is undesirable and it must be considered in realizing high precision control application. In this paper, the nonlinearities of McKibben muscle is characterized using empirical modeling with multiple correction functions such as shape irregularity and slenderness. A particle swarm optimization (PSO) method is used to determine the best parametric values of the proposed empirical with modified dynamic friction model. The LabVIEW and MATLAB platforms are used for data analysis, modeling and simulation. The results confirm that this model able to significantly characterize the nonlinearities of McKibben muscle while considering all dependencies. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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13 pages, 7511 KiB  
Article
A Mechatronics-Embedded Pneumatic Soft Modular Robot Powered via Single Air Tube
by Yu Zhang, Yubin Liu, Xin Sui, Tianjiao Zheng, Dongyang Bie, Yulin Wang, Jie Zhao and Yanhe Zhu
Appl. Sci. 2019, 9(11), 2260; https://doi.org/10.3390/app9112260 - 31 May 2019
Cited by 10 | Viewed by 3657
Abstract
Soft modular robots have advantages, including infinite degrees of freedom and various configurations. Most soft robots are actuated by inflating air pressure into their chambers. However, each chamber is connected to a tube that provides the air supply, which incurs drag and intertwining [...] Read more.
Soft modular robots have advantages, including infinite degrees of freedom and various configurations. Most soft robots are actuated by inflating air pressure into their chambers. However, each chamber is connected to a tube that provides the air supply, which incurs drag and intertwining problems that influence the robot’s motion. Moreover, the number of chambers directly affects the deformations and motion capabilities of the robot. Therefore, the crucial issue is the structure of a soft modular robot that can share an air source without reducing the number of chambers and can guarantee the deformations of the robot. In this paper, a novel mechatronics-embedded soft module was designed and manufactured, which has an air supply sharing function. Therefore, the soft modular robot can be powered via a single air tube. In addition, a wireless platform to control the air pressure of the module was built, and an experimental model was established to obtain the relationship between the deformation and pressure of the module. Four experiments were performed under different conditions. The experiments’ results indicate the bending capability of the module. Moreover, hooking object, twisting motion, and bionic gesture experiments demonstrate the validity of the module’s air pressure sharing function. Therefore, the air sharing supply approach proposed in this paper can be used as a reference to solve the tube drag problem of soft modular robots. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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10 pages, 3446 KiB  
Article
Single Leg Gait Tracking of Lower Limb Exoskeleton Based on Adaptive Iterative Learning Control
by Bin Ren, Xurong Luo and Jiayu Chen
Appl. Sci. 2019, 9(11), 2251; https://doi.org/10.3390/app9112251 - 31 May 2019
Cited by 14 | Viewed by 3148
Abstract
The lower limb exoskeleton is a wearable human–robot interactive equipment, which is tied to human legs and moves synchronously with the human gait. Gait tracking accuracy greatly affects the performance and safety of the lower limb exoskeletons. As the human–robot coupling systems are [...] Read more.
The lower limb exoskeleton is a wearable human–robot interactive equipment, which is tied to human legs and moves synchronously with the human gait. Gait tracking accuracy greatly affects the performance and safety of the lower limb exoskeletons. As the human–robot coupling systems are usually nonlinear and generate unpredictive errors, a conventional iterative controller is regarded as not suitable for safe implementation. Therefore, this study proposed an adaptive control mechanism based on the iterative learning model to track the single leg gait for lower limb exoskeleton control. To assess the performance of the proposed method, this study implemented the real lower limb gait trajectory that was acquired with an optical motion capturing system as the control inputs and assessment benchmark. Then the impact of the human–robot interaction torque on the tracking error was investigated. The results show that the interaction torque has an inevitable impact on the tracking error and the proposed adaptive iterative learning control (AILC) method can effectively reduce such error without sacrificing the iteration efficiency. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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13 pages, 6407 KiB  
Article
Model of a Coil-Reinforced Cylindrical Soft Actuator
by Takahiro Kanno, Shunya Ohkura, Osamu Azami, Tetsuro Miyazaki, Toshihiro Kawase and Kenji Kawashima
Appl. Sci. 2019, 9(10), 2109; https://doi.org/10.3390/app9102109 - 23 May 2019
Cited by 14 | Viewed by 3982
Abstract
A cylindrical soft actuator is suitable for applications in which pneumatic or hydraulic cylinders are conventionally used. In this report, we discuss the force output model of a spring-reinforced-type cylindrical soft actuator. This type of actuator outputs a larger force than the air [...] Read more.
A cylindrical soft actuator is suitable for applications in which pneumatic or hydraulic cylinders are conventionally used. In this report, we discuss the force output model of a spring-reinforced-type cylindrical soft actuator. This type of actuator outputs a larger force than the air pressure multiplied by the pressure-receiving area. We construct a quasi-static model to explore the reason for this phenomenon, based on the strength of materials. A thick-walled cylinder model with three boundary conditions was defined and analyzed. The model indicates that the rubber cylinder itself transmits pneumatic pressure and contributes to the output force. We also modeled the relationship between the pressure and the elongation of the soft actuator. Experiments were conducted to evaluate the proposed models. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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15 pages, 4622 KiB  
Article
Jumping with Expandable Trunk of a Metamorphic Quadruped Robot—The Origaker II
by Tengfei Li, Chunsong Zhang, Shengjie Wang and Jian S. Dai
Appl. Sci. 2019, 9(9), 1778; https://doi.org/10.3390/app9091778 - 29 Apr 2019
Cited by 8 | Viewed by 3244
Abstract
Most of the traditional quadruped robots are assembled with rigid trunks that make no active contributions to their locomotion performances. However, in the natural world, some quadrupeds expand their trunks when jumping. This paper proposes a metamorphic quadruped robot, named the Origaker II, [...] Read more.
Most of the traditional quadruped robots are assembled with rigid trunks that make no active contributions to their locomotion performances. However, in the natural world, some quadrupeds expand their trunks when jumping. This paper proposes a metamorphic quadruped robot, named the Origaker II, with an expandable trunk that can implement the motion of contracting-stretching. Benefitting from the expandable trunk, this robot achieves a longer jumping distance than that of the traditional quadruped robots. The structure of the robot is introduced. Its jumping motion is designed based on the observation of a frog. The effect of the expandable trunk on this robot will be mathematically analyzed. At last, contrast simulations are conducted to verify the benefits of the expandable trunk to the robot. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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23 pages, 17253 KiB  
Article
The Development of a Soft Robot Hand with Pin-Array Structure
by Hong Fu and Wenzeng Zhang
Appl. Sci. 2019, 9(5), 1011; https://doi.org/10.3390/app9051011 - 11 Mar 2019
Cited by 18 | Viewed by 3662
Abstract
This paper proposes a soft robot hand with pin-array structure and self-adaptive function, CTSA-II hand, where CTSA is the Cluster tube self-adaption. The CTSA-II hand is designed with a quite concise structure and consists of bases, a pin array, a spring array, and [...] Read more.
This paper proposes a soft robot hand with pin-array structure and self-adaptive function, CTSA-II hand, where CTSA is the Cluster tube self-adaption. The CTSA-II hand is designed with a quite concise structure and consists of bases, a pin array, a spring array, and a membrane. When the CTSA-II hand grasps an object, the pins will slide along the trajectory to conform to the profile of the object under the reaction force applied by the object, and thus the outer membrane will form a specific shape, and then the vacuum drives the CTSA-II hand to grasp the object. Theoretical analysis shows that the CTSA-II hand can generate enough grasping force and get good stability. Moreover, the optimization of its structure is achieved by studying the effects of specific parameters. The capture experimental results of the prototype show that the CTSA-II hand can realize self-adaptive grasping of different sizes and shapes with a high degree of fit and a high success rate. A series of research experiments show the influence of various factors on the grasping force, which verifies the results of the theoretical analysis with the CTSA-II hand. Compared to the traditional robot hand, the CTSA-II hand has good crawl performance, concise structure, small volume, and easy assembly. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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32 pages, 5834 KiB  
Review
Dielectric Elastomer Actuator for Soft Robotics Applications and Challenges
by Jung-Hwan Youn, Seung Mo Jeong, Geonwoo Hwang, Hyunwoo Kim, Kyujin Hyeon, Jihwan Park and Ki-Uk Kyung
Appl. Sci. 2020, 10(2), 640; https://doi.org/10.3390/app10020640 - 16 Jan 2020
Cited by 135 | Viewed by 21803
Abstract
This paper reviews state-of-the-art dielectric elastomer actuators (DEAs) and their future perspectives as soft actuators which have recently been considered as a key power generation component for soft robots. This paper begins with the introduction of the working principle of the dielectric elastomer [...] Read more.
This paper reviews state-of-the-art dielectric elastomer actuators (DEAs) and their future perspectives as soft actuators which have recently been considered as a key power generation component for soft robots. This paper begins with the introduction of the working principle of the dielectric elastomer actuators. Because the operation of DEA includes the physics of both mechanical viscoelastic properties and dielectric characteristics, we describe theoretical modeling methods for the DEA before introducing applications. In addition, the design of artificial muscles based on DEA is also introduced. This paper reviews four popular subjects for the application of DEA: soft robot hand, locomotion robots, wearable devices, and tunable optical components. Other potential applications and challenging issues are described in the conclusion. Full article
(This article belongs to the Special Issue Soft Robotics: New Design, Control, and Application)
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