A vacuum-driven inclined hexagonal prism soft-rigid hybrid contraction actuator inspired by Kresling origami pattern and with low driving pressure, high contraction ratio, and fast response was proposed. The advantages of soft-rigid hybrid vacuum contraction actuators over conventional positive-type oscillators were investigated. Under 30 kPa vacuum pressure, the actuator can realize a torsional angle of 87°, contraction ratio of 59%, contracting response time of 0.2 s, and restoring response time of 0.42 s. The design and fabrication of the proposed actuator were discussed. A mathematical model treating all creases as a combination of linear and torsion springs, which is firstly considered compared with previously proposed models of Kresling origami-based actuators, was established to predict the output performance. The excellent output force prediction performance of the proposed method was validated experimentally. To investigate the application potential of the proposed modular actuator, six actuators were assembled on a pipe-crawling robot that can crawl in horizontal, vertical, elbow rigid pipes as well as flexible pipes with inner diameters ranging from 55 to 71 mm. The robot achieved a maximum crawling velocity of 34.8 mm s⁻¹ (0.226 body lengths per second) and maximum load of 1000 g (12.5 times its own weight) in tests. Thus, the excellent application potential of the proposed actuator was validated.

In wearable applications, traditional pneumatic artificial muscles (PAMs) cannot fully satisfy the requirements of safe and sufficient interaction with the human body. The requirements include high contraction ratio, self-contained sensing, reconfiguration, locking abilities, and avoidance of the squeezing force acting on the human tissue. In this letter, a reconfigurable self-sensing pneumatic artificial muscle (RSPAM) based on modular multi-chamber soft actuator with locking ability is developed, which provides an alternative that can satisfy all the requirements for the wearable applications. The contraction principle of the RSPAM, which includes transforming the expansion of the soft actuator into contraction by fabric winding, has an inherently high contraction ratio and completely avoids squeezing of human tissue. Self-sensing of contraction stroke based on liquid metal and locking ability based on positive pressure jamming are integrated. A driving force and contraction ratio of 70.14 N and of 71% were validated at 3 bar air pressure. Modular design of the actuator makes it possible to change the configuration by adjusting the actuator amount and the fabric length according to the application. In addition, the actuator unit can move on the fabric by itself, enabling a noteworthy self-adjustment ability for the muscle. The displacement self-sensing ability is verified through square-wave tracking experiments with closed-loop control. Finally, a preliminary test of assisting elbow movement verifies that the RSPAM can reduce 53.05% of the muscle fatigue.

Pneumatic artificial muscles are extensively employed in soft wearable robotic systems to assist the movements of human joints. Nevertheless, conventional pneumatic artificial muscles make it difficult to change their configuration to adapt to different human joints. Moreover, a mismatching of assistive parameters and human motions causes poor adaptability or limited assistive performance. This study introduces a reconfigurable exomuscle system that employs the best evaluated parameters to assist hip flexion or ankle plantarflexion during walking. A set of the best evaluated parameters is determined from nine conditions with the objective of minimizing muscle activation in treadmill walking trials. Nine conditions represent different assistance timings of the exomuscle contraction and extension, which are triggered by foot plantar pressure. The system's configuration can be altered from a series mode to a parallel mode within 7 mins. Assistive performance is validated through human subject testing of ten participants in both indoor and outdoor environments. The average reduction in metabolic cost for hip flexion assistance is 9.99%, whereas the average decrease for ankle plantarflexion assistance is 7.91% in treadmill walking. Results of an outdoor environment test indicate that metabolic costs can be reduced. The system offers an alternative method to facilitate the application of reconfigurable portable devices in real-world situations.

This paper proposes a pneumatic artificial muscle based on a novel winding method. By this method, the inflation of silicone tubes is transformed to the contraction of muscle, whereas the expansion keeps on one side of the muscle, i.e., the expansion of the actuator does not affect the object close to it. Hence the muscle is great for wearable robots without squeezing on the user’s skin. Through necessary simplification, the contraction ratio model and force model are proposed and verified by experiments. The prototype of this paper has a maximum contraction ratio of 35.8% and a maximum output force of 12.24 N with only 5 mm thickness. The high compatibility proves it excellent to be the alternative for wearable robots.

Some special tasks require human operations and cannot be performed by robots or other autonomous equipment, such as special industrial assembly and surgical procedures in small and crowded spaces. Workers/surgeons in these cases tend to have physical fatigue. In this study, a novel variable-stiffness joint based on positive pressure was proposed, and a torque model was established. The locking torque variation, step response, and energy consumption were evaluated in comparison with a torque motor. A lockable lower-limb exoskeleton based on the variable-stiffness joint was developed, and wearable tests were conducted to evaluate a voice recognition interface and supporting performance. The locking torque of the variable-stiffness joint could be continuously varied from 0 Nm to 26 Nm with the air pressure ranging from 1.6 bar to 5.5 bar. The settling time was 0.328 s in the step response experiment. With a load of 6 Nm, the variable-stiffness joint can realize an energy consumption reduction of 75.01% compared with using a torque motor. Moreover, the lockable lower-limb exoskeleton can realize a 35–60% reduction in the average muscle activation in each subject (aged 22–57) to maintain squatting postures at three different knee angles (paired t-test, P < 0.01). The proposed exoskeleton system has good mobility, low energy consumption, and easy-to-control features, showing great potential in supporting the weight of workers/surgeons during long-term operations.

This letter presents a lockable upper-limb exoskeleton to reduce the physical fatigue of laborers/surgeons operating with upper limbs maintaining fixed posture for long time. A novel structure design integrating the jamming and engagement mechanisms that can provide locking of flexion and adduction movements of upper arm without affecting the motion space is proposed. An air-pressure waist bag with a voice control interface is developed, giving good portability and user convenience to the exoskeleton. The system is validated in experiments, indicating a locking torque as large as 6 Nm with 3.5 bar air pressure. Locking and unlocking settling times of the jamming mechanism are 0.09 s and 0.10 s, meaning nearly no delay can be felt by users for the switching. Moreover, surface electromyography (EMG) signal tests demonstrate that the proposed exoskeleton can significantly reduce muscle activation of randomly selected subjects by 25%--73%. Compared with commercially-available passive exoskeletons, proposed system has a lower weight, much larger and adjustable locking torque owing to the specially designed jamming mechanism. The exoskeleton presents good compliance, great flexibility, and hands free human-machine interface, showing good potential for physical fatigue reduction of laborers/surgeons over long-term operations.