Soft robotics最新文献

Due to their exceptional adaptability, inherent compliance, and high flexibility, soft actuators have significant advantages over traditional rigid actuators in human-machine interaction and in grasping irregular or fragile objects. Most existing soft actuators are designed using preprogramming methods, which schedule complex motions into flexible structures by correctly designing deformation constraints. These constraints restrict undesired deformation, allowing the actuator to achieve the preprogrammed motion when stimulated. Therefore, these actuators can only achieve a certain type of motion, such as extension, bending, or twisting, since it is impossible to adjust the deformation constraints once they are embedded into the structures. In this study, we propose the use of variable stiffness materials, such as shape memory polymer (SMP), in the structural design of soft actuators to achieve variable stiffness constraints. A reconfigurable soft helical actuator with a variable stiffness skeleton is developed based on this concept. The skeleton, made of SMP, is encased at the bottom of a fiber-reinforced chamber. In its high-stiffness state, the SMP constrains the deformation toward the skeleton when the actuator is pressurized. This constraint is removed once the SMP skeleton is heated, endowing the actuator with the ability to switch between bending and helical motion in real-time. A theoretical model is proposed to predict the behavior of the actuator when driven by pressure, and experiments are conducted to verify the model's accuracy. In addition, the influence of different design parameters is investigated based on experimental results, providing reference guidelines for the design of the actuator.

Usability and functionality are important when designing hand-wearable robots; however, satisfying both indicators remains a challenging issue, even though researchers have made important progress with state-of-the-art robot components. Although hand-wearable robots require sufficient actuators and sensors considering their functionality, these components complicate the robot. Further, robot compliance should be carefully considered because it affects both indicators. For example, a robot's softness makes it compact (improving usability) but also induces inaccurate force transmission (impacting functionality). To address this issue, we present in this paper a tendon-driven, hybrid, hand-wearable robot, named Exo-Glove Shell. The proposed robot assists in three primitive motions (i.e., thumb opposition motion, which is known as one of the most important hand functions, and flexion/extension of the index/middle fingers) while employing only four actuators by using an under-actuation mechanism. The Exo-Glove Shell was designed by combining a soft robotic body with rigid tendon router modules. The use of soft garments enables the robot to be fitted well to users without customization or adjustment of the mechanisms; the metal routers facilitate accurate force transmission. User tests conducted with an individual with a spinal cord injury (SCI) found that the robot could sufficiently and reliably assist in three primitive motions through its four actuators. The research also determined that the robot can assist in various postures with sufficient stability. Based on the grasp stability index proposed in this paper, user stability-when assisted by the proposed robot-was found to be 4.75 times that of an SCI person who did not use the Exo-Glove Shell.

Many organisms move directly toward light for prey hunting or navigation, which is called phototaxis. Mimicking this behavior in robots is crucially important in the energy industry and environmental exploration. However, the phototaxis robots with rigid bodies and sensors still face challenges in adapting to unstructured environments, and the soft phototaxis robots often have high requirements for light sources with limited locomotion performance. Here, we report a 3.5 g soft microrobot that can perceive the azimuth angle of light sources and exhibit rapid phototaxis locomotion autonomously enabled by three-dimensional flexible optoelectronics and compliant shape memory alloy (SMA) actuators. The optoelectronics is assembled from a planar patterned flexible circuit with miniature photodetectors, introducing the self-occlusion to light, resulting in high sensing ability (error < 3.5°) compared with the planar counterpart. The actuator produces a straightening motion driven by an SMA wire and is then returned to a curled shape by a prestretched elastomer layer. The actuator exhibits rapid actuation within 0.1 s, a significant degree of deformation (curvature change of ∼87 m^-1) and a blocking force of ∼0.4 N, which is 68 times its own weight. Finally, we demonstrated the robot is capable of autonomously crawling toward a moving light source in a hybrid aquatic-terrestrial environment without human intervention. We envision that our microrobot could be widely used in autonomous light tracking applications.

Sound is a rich information medium that transmits through air; people communicate through speech and can even discern material through tapping and listening. To capture frequencies in the human hearing range, commercial microphones typically have a sampling rate of over 40 kHz. These accessible acoustic technologies are not yet widely adopted for the explicit purpose of giving robots a sense of touch. Some researchers have used sound to sense tactile information, both monitoring ambient soundscape and with embedded speakers and microphones to measure sounds within structures. However, these options commonly do not provide a direct measure of steady state force or require electronics integrated somewhere near the contact location. In this work, we present AcousTac, an acoustic tactile sensor for electronics-free, force-sensitive soft skin. Compliant silicone caps and plastic tubes compose the resonant chambers that emit pneumatic-driven sound measurable with a conventional off-board microphone. The resulting frequency changes depend on the external loads on the compliant endcaps. The compliant cap vibrates with the resonant pressure waves and is a nonidealized boundary condition, initially producing a nonmonotonic force response. We characterize two solutions-adding a distal hole and mass to the cap-resulting in monotonic and nonhysteretic force readings with this technology. We can tune each AcousTac taxel to specific force and frequency ranges, based on geometric parameters including tube length, and thus uniquely sense each taxel simultaneously in an array. We demonstrate AcousTac's functionality on two robotic systems: a 4-taxel array and a 3-taxel astrictive gripper. Simple to implement with off-the-shelf parts, AcousTac is a promising concept for force sensing on soft robotic surfaces, especially in situations where electronics near the contact are not suitable. Equipping robots with tactile sensing and soft skin provides them with a sense of touch and the ability to safely interact with their surroundings.

The field of soft robotics is rapidly evolving, and there is a growing interest in developing soft robots with bioinspired features for use in various applications. This research presented the design and development of 3D-printed origami actuators for a soft robot with amphibious locomotion and tongue hunting capabilities. Two different types of programmable origami actuators were designed and manufactured, namely Z-shaped and twist tower actuators. In addition, two actuator variations were developed based on the Z-shaped actuator, including the pelvic fin and the coiling/uncoiling types. The Z-shaped actuators were used for the rear legs to facilitate the locomotion of the water-like frogs. Meanwhile, the twisted tower actuators were used for the rotation joints in the forelegs and for locomotion on land. The pelvic fin actuator was developed to imitate the land locomotion of the mudskipper, and the coiling/uncoiling actuator was designed for tongue hunting motion. The origami actuators and soft robot prototype were tested through a series of experiments, which showed that the robot was capable of efficiently moving in water and on land and performing tongue hunting motions. Our results demonstrate the effectiveness of these actuators in producing the desired motions and provide insights into the potential of applying 3D-printed origami actuators in the development of soft robots with bioinspired features.

Although soft robots show safer interactions with their environment than traditional robots, soft mechanisms and actuators still have significant potential for damage or degradation particularly during unmodeled contact. This article introduces a feedback strategy for safe soft actuator operation during control of a soft robot. To do so, a supervisory controller monitors actuator state and dynamically saturates control inputs to avoid conditions that could lead to physical damage. We prove that, under certain conditions, the supervisory controller is stable and verifiably safe. We then demonstrate completely onboard operation of the supervisory controller using a soft thermally actuated robot limb with embedded shape memory alloy actuators and sensing. Tests performed with the supervisor verify its theoretical properties and show stabilization of the robot limb's pose in free space. Finally, experiments show that our approach prevents overheating during contact, including environmental constraints and human touch, or when infeasible motions are commanded. This supervisory controller, and its ability to be executed with completely onboard sensing, has the potential to make soft robot actuators reliable enough for practical use.

This article focuses on haptic localization of very lightweight and delicate objects while applying a contact force >5000 times lower than the weight of the object. A soft whisker integrated with a Force/Moment (F/M) sensor at the base, and a novel reconstruction algorithm have been proposed for this purpose. Initially, the mathematical relationships between the deformations of the whisker and the F/M sensor outputs were used to reconstruct the shape of the whisker and the position of the touched object. The Cosserat rod theory was used under the assumption that only one contact point occurs during the exploration, and friction effects are negligible. A new methodology we called moment only reading (MOR) has been tested, verified, and compared with previous methods that employed Force and Moment Readings (FMR). Experimental investigations revealed that the spatial position estimation error of the MOR method was confined within 13 mm, when the force applied ranged between 0.001 and 0.01 N. Moreover, the comparison with FMR demonstrated that MOR is capable of retrieving the position of objects even when the force readings drop below the force resolution of the sensor. Eventually, the MOR method has been applied to demonstrate the localization and grasping, with a soft gripper, of delicate crops like tomatoes and strawberries.

In recent years, soft robotic grippers have emerged as a promising solution for versatile and safe manipulation of objects in various fields. However, precise force control is critical, especially when handling delicate or fragile objects, to avoid excessive grip force application or to prevent object slippage. Herein, we propose a novel three-degree-of-freedom force sensor incorporated within a soft robotic gripper to realize stable grasping with force feedback. The proposed optical sensor employs lightweight and compact optical fibers, thereby allowing for cost-effective fabrication, and a robust sensing system that is immune to electromagnetic fields. By innervating the soft gripper with optical fibers, a durable system is achieved with the fibers functioning as a strengthening layer, thereby eliminating the need for embedding an external stiffening structure for efficient bending actuation. The innovative contact-based light loss sensing mechanism allows for a robust and stable sensing mechanism with low drift (<0.1% over 9000 cycles) that can be applied to soft pneumatic bending grippers. We used the developed sensor-incorporated soft gripper to grasp various objects, including magnetic materials, and achieved slip detection along with grip force feedback without any signal interference. Overall, this study proposes a robust measuring multi-degree-of-freedom force sensor that can be incorporated into grippers for improved grasping stability.

Soft gastric simulators are in vitro biomimetic modules that can reproduce the antral contraction waves (ACWs). Along with providing information concerning stomach contents, stomach simulators enable experts to evaluate the digestion process of foods and drugs. Traditionally, open-loop control approaches were implemented on stomach simulators to produce ACWs. Constructing a closed-loop control system is essential to improve the simulator's ability to imitate ACWs in additional scenarios and avoid constant tuning. Closed-loop control can enhance stomach simulators in accuracy, responding to various food and drug contents, timing, and unknown disturbances. In this article, a new generation of anatomically realistic soft pneumatic gastric simulators is designed and fabricated. The presented simulator represents the antrum, the lower portion of the stomach where ACWs occur. It is equipped with a real-time feedback system to implement diverse closed-loop controllers on demand. All the details of the physical design, fabrication, and assembly process are discussed. Also, the measures taken for the mechatronics design and sensory system are highlighted in this article. Through several implementation algorithms and techniques, three closed-loop controllers, including model-based and model-free schemes are designed and successfully applied on the presented simulator to imitate ACWs. All the experimental outcomes are carefully analyzed and compared against the biological counterparts. It is demonstrated that the presented simulator can serve as a reliable tool and method to scrutinize digestion and promote novel technologies around the human stomach and the digestion process. This research methodology can also be utilized to develop other biomimetic and bioinspired applications.

The increasing demand for inspection, upkeep, and repair of pipeline and tunnel infrastructures has catalyzed research into the creation of robots with superior flexibility, adaptability, and load-bearing capacities. This study introduces an autonomous soft robot designed for navigating both straight and curved pipelines of 90 mm diameter. The soft robot is enabled by an elongation pneumatic actuator (EPA) as its body and multiple radial expansion pneumatic actuators (REPAs) as its feet to provide adhesion and support on the pipe walls. It achieves a horizontal movement speed of 1.27 mm/s and ascends vertically at 0.39 mm/s. An integrated control mechanism, merging both pneumatic and electrical systems is employed to facilitate unrestrained movement. A novel control tactic has been formulated to ensure synchronized coordination between the robot's body deformation and leg anchoring, ensuring stable movement. This soft robot demonstrates remarkable mobility metrics, boasting an anchoring strength of over 100 N, a propelling force of 43.8 N when moving vertically, and a pulling strength of 31.4 N during navigation in curved pipelines. It can carry a camera to capture the internal view of the pipe and remove obstacles autonomously. The unconstrained and autonomous movement of the untethered soft robot presents new opportunities for various applications at different scales.