Materials for Smart Soft Actuator Systems

The expensive nature of currently used materials in the soft robotic industry demands the consideration of alternative materials for fabrication. This work investigates the performance of RTV-2 grade silicone rubber for fabrication of a soft actuator. Initially, a cylindrical actuator is fabricated using this material and its performance is experimentally assessed for different pressures. Further, parametric variations of the effect of wall thickness and inflation pressure are studied by numerical methods. Results show that, both wall thickness and inflation pressure are influential parameters which affect the elongation behaviour of the actuator. Thin (1.5 mm) sectioned actuators produced 76.97% more elongation compared to thick sectioned, but the stress induced is 89.61 % higher. Whereas, the thick sectioned actuator (6 mm) showed a higher load transmitting capability. With change in wall thickness from 1.5 mm to 6 mm, the elongation is reduced by 76.97 %, 38.35 %, 21.05 % and 11.43 % at pressure 100 kPa, 75 kPa, 50 kPa and 25 kPa respectively. The induced stress is also found reduced by 89.61 %, 86.66 %, 84.46 % and 68.68 % at these pressures. The average load carrying capacity of the actuator is found to be directly proportional to its wall thickness and inflation pressure.

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Actuation and dynamic mechanical characteristics of a core free flat dielectric electro-active polymer soft actuator

JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES ◽

10.15282/jmes.14.4.2020.08.0582 ◽

2020 ◽

Vol 14 (4) ◽

pp. 7396-7404

Author(s):

Abdul Malek Abdul Wahab ◽

Emiliano Rustighi ◽

Zainudin A.

Keyword(s):

Theoretical Model ◽

Resonance Frequency ◽

Dynamic Testing ◽

Experimental Results ◽

Percentage Error ◽

Initial Tension ◽

Average Percentage ◽

Soft Actuator ◽

Average Percentage Error ◽

Mechanical Dynamics

Various complex shapes of dielectric electro-active polymer (DEAP) actuator have been promoted for several types of applications. In this study, the actuation and mechanical dynamics characteristics of a new core free flat DEAP soft actuator were investigated. This actuator was developed by Danfoss PolyPower. DC voltage of up to 2000 V was supplied for identifying the actuation characteristics of the actuator and compare with the existing formula. The operational frequency of the actuator was determined by dynamic testing. Then, the soft actuator has been modelled as a uniform bar rigidly fixed at one end and attached to mass at another end. Results from the theoretical model were compared with the experimental results. It was found that the deformation of the current actuator was quadratic proportional to the voltage supplied. It was found that experimental results and theory were not in good agreement for low and high voltage with average percentage error are 104% and 20.7%, respectively. The resonance frequency of the actuator was near 14 Hz. Mass of load added, inhomogeneity and initial tension significantly affected the resonance frequency of the soft actuator. The experimental results were consistent with the theoretical model at zero load. However, due to inhomogeneity, the frequency response function’s plot underlines a poor prediction where the theoretical calculation was far from experimental results as values of load increasing with the average percentage error 15.7%. Hence, it shows the proposed analytical procedure not suitable to provide accurate natural frequency for the DEAP soft actuator.

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High-cycle-life and high-loading copolymer network with potential application as a soft actuator

Materials & Design ◽

10.1016/j.matdes.2019.108010 ◽

2019 ◽

Vol 182 ◽

pp. 108010 ◽

Cited By ~ 6

Author(s):

Hafeez Ur Rehman ◽

Yujie Chen ◽

Mikael S. Hedenqvist ◽

Radan Pathan ◽

Hezhou Liu ◽

...

Keyword(s):

Potential Application ◽

Cycle Life ◽

High Loading ◽

Soft Actuator ◽

Copolymer Network

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Sensuator: A Hybrid Sensor–Actuator Approach to Soft Robotic Proprioception Using Recurrent Neural Networks

Actuators ◽

10.3390/act10020030 ◽

2021 ◽

Vol 10 (2) ◽

pp. 30

Author(s):

Pornthep Preechayasomboon ◽

Eric Rombokas

Keyword(s):

Neural Networks ◽

Recurrent Neural Networks ◽

Linear Models ◽

Open Loop ◽

Proof Of Concept ◽

State Estimator ◽

Loop Control ◽

Practical Applications ◽

Soft Actuator ◽

The Cost

Soft robotic actuators are now being used in practical applications; however, they are often limited to open-loop control that relies on the inherent compliance of the actuator. Achieving human-like manipulation and grasping with soft robotic actuators requires at least some form of sensing, which often comes at the cost of complex fabrication and purposefully built sensor structures. In this paper, we utilize the actuating fluid itself as a sensing medium to achieve high-fidelity proprioception in a soft actuator. As our sensors are somewhat unstructured, their readings are difficult to interpret using linear models. We therefore present a proof of concept of a method for deriving the pose of the soft actuator using recurrent neural networks. We present the experimental setup and our learned state estimator to show that our method is viable for achieving proprioception and is also robust to common sensor failures.

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Towards Ultrasonically Actuated Programmable Polymorphic Soft Actuator

2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS) ◽

10.1109/mems51782.2021.9375438 ◽

2021 ◽

Author(s):

Ju Hong Nam ◽

Youngju Oh ◽

Eunjeong Byun ◽

Eunseo Joo ◽

Soryeong Jeong ◽

...

Keyword(s):

Soft Actuator

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Soft Gripper Design Based on the Integration of Flat Dry Adhesive, Soft Actuator, and Microspine

IEEE Transactions on Robotics ◽

10.1109/tro.2020.3043981 ◽

2021 ◽

pp. 1-16 ◽

Cited By ~ 1

Author(s):

Qiqiang Hu ◽

Erbao Dong ◽

Dong Sun

Keyword(s):

Dry Adhesive ◽

Soft Actuator

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Control of an IPMC Soft Actuator Using Adaptive Full-Order Recursive Terminal Sliding Mode

Actuators ◽

10.3390/act10020033 ◽

2021 ◽

Vol 10 (2) ◽

pp. 33

Author(s):

Romina Zarrabi Ekbatani ◽

Ke Shao ◽

Jasim Khawwaf ◽

Hai Wang ◽

Jinchuan Zheng ◽

...

Keyword(s):

Sliding Mode ◽

External Disturbance ◽

Tracking Error ◽

Working Environment ◽

Parametric Uncertainties ◽

Metal Composite ◽

External Disturbances ◽

Terminal Sliding Mode ◽

Positioning Accuracy ◽

Soft Actuator

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection.

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Characterisation and Control of a Woven Biomimetic Actuator for Wearable Neurorehabilitative Devices

Actuators ◽

10.3390/act10020037 ◽

2021 ◽

Vol 10 (2) ◽

pp. 37

Author(s):

Vaughan Murphy ◽

Brandon P. R. Edmonds ◽

Ana Luisa Trejos

Keyword(s):

Performance Metrics ◽

Woven Fabric ◽

Total Force ◽

Control Methods ◽

Soft Actuator ◽

Sewing Thread ◽

And Control ◽

Fabric Mesh ◽

Biomimetic Actuator ◽

Multiple Units

Twisted coiled actuators (TCAs) are a type of soft actuator made from polymer fibres such as nylon sewing thread. As they provide motion in a compact, lightweight, and flexible package, they provide a solution to the actuation of wearable mechatronic devices for motion assistance. Their limitation is that they provide low total force, requiring them to actuate in parallel with multiple units. Previous literature has shown that the force and stroke production can be improved by incorporating them into fabric meshes. A fabric mesh could also improve the contraction efficiency, strain rate, and user comfort. Therefore, this study focused on measuring these performance metrics for a set of TCAs embedded into a woven fabric mesh. The experimental results show that the stroke of the actuators scaled linearly with the number of activated TCAs, achieving a maximum applied force of 11.28 N, a maximum stroke of 12.23%, and an efficiency of 1.8%. Additionally, two control methods were developed and evaluated, resulting in low overshoot and steady-state error. These results indicate that the designed actuators are viable for use in wearable mechatronic devices, since they can scale to meet different requirements, while being able to be accurately controlled with minimal additional components.

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