Soft robots have been significantly studied in recent decades, and among their key components are soft actuators. Vacuum is one of the main drivers of soft actuators. In this study, we propose a novel cylindrical soft vacuum actuator (CSVA) consisting of a top layer, bottom layer, and cylindrical internal chamber. Under a vacuum, the bottom layer was concaved into the internal chamber. A simplified analytical model was established to analyze the relationship between the vacuum pressure and the deformation height of the bottom layer. A validation experiment was conducted to verify the effectiveness of the proposed analytical model. The potential applications of the CSVA in the design of soft robots were also explored. A jellyfish-inspired swimming robot, an octopus-inspired suction cup, and a soft–rigid gripper were designed according to the concave deformation of the bottom layer. Then, the swimming speed of the swimming robot, the adsorption force of the suction cup, and the grasping capability of the soft–rigid gripper were investigated. The experimental results show that the maximum swimming speed of the swimming robot is 55.3 mm s−1 at a flapping frequency of 0.6 Hz. The adsorption forces of the suction cup both in air and underwater are 16.8 N and 17.5 N, respectively. The soft–rigid gripper with a pinching-grasping mode can grasp objects of various shapes and sizes in air and underwater. The experimental results demonstrate the feasibility of the soft vacuum actuator in the design of various soft robots.

Soft robot has been one significant study in recent decades and soft gripper is one of the popular research directions of soft robot. In a static gripping system, excessive gripping force and large deformation are the main reasons for damage of the object during the gripping process. For achieving low-damage gripping to the object in static gripping system, we proposed a soft-rigid gripper actuated by a linear-extension soft pneumatic actuator in this study. The characteristic of the gripper under a no loading state was measured. When the pressure was >70 kPa, there was an approximately linear relation between the pressure and extension length of the soft actuator. To achieve gripping force and fingertip displacement control of the gripper without sensors integrated on the finger, we presented a non-contact sensing method for gripping state estimation. To analyze the gripping force and fingertip displacement, the relationship between the pressure and extension length of the soft actuator in loading state was compared with the relationship under a no-loading state. The experimental results showed that the relative error between the analytical gripping force and the measured gripping force of the gripper was ≤2.1%. The relative error between analytical fingertip displacement and theoretical fingertip displacement of the gripper was ≤7.4%. Furthermore, the low damage gripping to fragile and soft objects in static and dynamic gripping tests showed good performance of the gripper. Overall, the results indicated the potential application of the gripper in pick-and-place operations.

Soft pneumatic actuators (SPAs) play an important role in leading the development of soft robotics. However, due to the inherent characteristics of soft materials, the low driving force limits the application of SPAs. This study presents a high-force soft pneumatic bending actuator (SPBA) that consists of a spring, an eccentric silicone cylinder, and a limiting fiber. Based on the Neo-Hookean model, a theoretical model is established to predict the relationship between the bending angle and pressure of SPBA. Furthermore, we characterize the performance of SPBA in terms of the bending capability, tip force, as well as response time. The results demonstrate the effectiveness of the theoretical model, as well as the high tip force (10.2 N) and fast response capability of SPBA. Finally, SPBAs are used to construct a three-finger soft gripper. The load capacity of the gripper is proofed, which indicates that the gripping force of the gripper increases with the pressure of the fingers and the diameter of the object. The gripping test of the gripper is performed. The result shows that the gripper with pinching mode can grip objects with various sizes and shapes in the air and underwater, and the gripper with enveloping mode can grip objects with weight up to 1.25 kg.

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Soft crawling robots have been significantly studied in recent decades. However, moving in amphibious environment, high payload capability, and passing through complex ground have always been challenges for soft crawling robots. For these problems, this article presents an amphibious soft-rigid wheeled crawling robot (SRWCR) consists of a soft-rigid body actuated by two soft pneumatic actuators (SPAs), four wheels, and four annular soft bladders (ASBs) as brakes. By programming the actuation sequences of the two SPAs and four ASBs, SRWCR can achieve two basic modes of locomotion: linear motion and turning. Based on the energy conservation law, we have developed analytical models to interpret the static actuation performance of SPA, including linear and bending deformations. Furthermore, with the help of fast response and waterproof of SPA and ASB, SRWCR can achieve a linear speed of 14.97 mm/s, a turning speed of 5.63°/s, and an underwater locomotion speed of 13 mm/s, which demonstrates the excellent locomotion performance of SRWCR in amphibious environment. In addition, SRWCR can also achieve multiple impressive functions, including carrying a payload of 2 kg at the moving speed of 11.18 mm/s, passing through various complex ground such as the grass ground and sand ground, and so on, obstacle navigation in confined space. Compared with the existing soft crawling robots, with the help of the soft-rigid body and wheeled structure, SRWCR has the best payload and passing capability, which indicates the potential advantage of SRWCR in the design of functional robots.