Soft Actuators for Soft Robotic Applications: A Review

Abstract

The compliant, continuum, and configurable robotics field in general has gained growing interest in the past years especially with the exciting advances in artificial intelligence technology, [1] which could enable various valuable applications ranging from manufacturing to safety and healthcare. [2,3] Soft robots are of notable interest because, unlike their rigid counterpart, they can easily deform while being mechanically resilient, [4,5] adapt to the outer environment without harm to humans, [6] and finally, enable low-cost manufacturing. [7] For robots to interact with the outer environment and complete tasks, a set of sensors and actuators need to be integrated into the system. Soft robots, in specific, present additional challenges because their sensing and actuation devices are generally highly integrated within the body of the robot and its whole functionality. These challenges become even more critical when the soft robot is scaled down to sub-centimeter size as the sensing, power, and data analysis units are moved off-board. As a result, miniaturized soft actuators that respond to various stimuli and show large deformations in addition to mechanical resilience are crucial. These would be particularly promising for application in artificial muscles, microrobots, and micro-manipulators. [8-10] Active and soft materials are promising for this task as they can be actuated through various external stimuli, such as photons, thermal, magnetic and/or electric field. Such materials range from particles, to polymers (either electroactive or shape memory), papers, fluids, shape memory alloys (SMAs), liquid metals, hydrogels, 2D materials, or a combination of these. [6-25] Nevertheless, some materials can be more suitable for a specific set of applications than others; for instance, materials stimulated by the near-infrared (NIR) spectrum are promising for biomedical applications, whereas sunlight-stimulated materials are suitable for nature-inspired soft robots used in outside environments. Various useful metrics are generally used to assess the performance of the actuators; these include the generated stress and strain, Young's modulus or measured stiffness, in addition to their power, work, energy, and force density. In this Review article, however, we focus on the application of the soft actuators in soft robotics where the reported metrics include mode and speed of actuation (or locomotion), power, voltage, current (of the driving signal), lifting force, and weight among others. In this Review article, different active materials that have been developed and used in soft actuators for soft robotics are discussed and grouped by the stimulus that generates the actuation response as shown in Figure 1. The physics of operation, resulting deformations, mechanical resilience, and their pros and cons are presented with a focus on the applications of the different soft

Recent Progress on Flexible Capacitive Pressure Sensors: From Design and Materials to Applications

“…Over the last two decades, wearable electronic devices have been trending due to the involvement and advancement of different research areas such as advanced manufacturing processes, computational mechanics, material technologies, miniaturization of different electronic components, and wireless communication. [ 177–179 ] Wearable sensors and actuators play a vital role from healthcare monitoring [ 42,121,180–186 ] and human‐computer interaction [ 161,182,183,185–189 ] to consumer electronics applications. [ 185,186,190,191 ] Researchers utilized different fabrication techniques (i.e., both conventional and emerging) to design smart electronic skin which can be tagged/deployed/placed on different non‐curvilinear surfaces for analysis of different parameters, including pressure.…”

“…[ 177–179 ] Wearable sensors and actuators play a vital role from healthcare monitoring [ 42,121,180–186 ] and human‐computer interaction [ 161,182,183,185–189 ] to consumer electronics applications. [ 185,186,190,191 ] Researchers utilized different fabrication techniques (i.e., both conventional and emerging) to design smart electronic skin which can be tagged/deployed/placed on different non‐curvilinear surfaces for analysis of different parameters, including pressure. [ 121,192–196 ] Diverse applications of wearable flexible capacitive pressure sensors are reviewed for healthcare, human–computer interaction, and consumer/portable electronics.…”

Finite Element Modeling of Soft Fluidic Actuators: Overview and Recent Developments

“…Recent review papers have covered different aspects of soft robotics design, [8,41] fabrication, [9,82] biological inspiration, [83,84] locomotion, [85] actuation methods, [86,87] sensing, [88,89] kinematic modeling, [52] control, [90,91] stiffening techniques, [92] and biomedical applications. [93,94] Despite the number of articles which use FEM, there is very little comparison of methods or guidelines for successful modeling.…”

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

“…Soft actuators are made of materials, which can deform in response to external forces and thermal stresses. Such materials can be in the form of particles, polymers, fluids, shape memory alloys (SMAs), liquid metals, hydrogels, or a combination of these [1]. Their favourable characteristics, such as low actuating voltage (<5 V), high power efficiency and biocompatibility make them suitable for soft mechatronics and robotic applications [2,3].…”

“…Given the IPMC system in(1) and the control law(21), there exists a positive number b i in(5) such thatb i ≤ b i (i = 0, 1, 2, 3) always holds.Proof of Lemma 1 is provided in Appendix A. Consider the IPMC system in (1), then the tracking error e under the AFORTSM controller in (21) will converge from any initial condition to zero in finite time.Proof.…”