In-flight high-speed object capturing is crucial in nature to improve survival and adaptation to the environment, such as the predation of frogs, leopards, and eagles. Despite its ubiquitousness in nature, capturing fast-moving objects is extremely challenging in engineering implementations. In this paper, we report an ultrafast gripper based on tunable bistable structures. Different from current designs which are only suitable for objects with certain speed ranges once the grippers are fabricated, the working range of object speed of the proposed gripper could be reprogrammed by controlling the sensitivity of the structures. We present the design and fabrication of the proposed gripper in detail. A theoretical model is introduced to construct the energy landscape of the structures and the force response of the gripper when programmed to different states. The results show that in the original state, the gripper is capable of capturing a flying table tennis ball with a high speed of 15 m/s in only 6 ms. When the proposed gripper is controlled to the ultra-sensitive state, a flying ball with only 1 m/s could also be captured. This work broadens the frontiers of in-flight capturing design, and we envision broader promising applications.

This paper presents a soft actuator inspired by origami and a tunable strain limiting layer, which is proposed for reconfigurable soft robotic grasping. Main structure of the actuator is based on Miura origami which generates extension under pressurized air while a limiting layer with tunable length enables the actuator with different motion patterns. By driving the limiting layer through a servo motor, the range of motion and trajectory of the actuator can be pre-programed and the gripper’s grasping range will be affected accordingly. This paper discusses the design, fabrication, analysis and experimental verification of the actuator. Then grasping performance of the gripper under objects of different shapes, sizes, and weights is experimentally evaluated. The reconfigurable soft gripper can be applied as an end-effector to accomplish adaptive grasping tasks with various targets.

Soft robotic gloves have shown great advantages in assisting individuals with hand pathologies to perform continuous exercises to restore their hand functions, which could considerably accelerate the rehabilitation process and reduce the costs. However, single rehabilitation mode, difficulty in achieving multiple degrees-of-freedom (DoF) motion, and the lack of high-fidelity feedback still challenge the development of soft robotic gloves. In this paper, we propose a novel design of a robotic glove based on soft-rigid hybrid joint actuators and minimal clutches. We first introduce structures and working principles of the proposed bending joint actuator in detail and then characterize the single joint actuator. Furthermore, we present a performance evaluation of the whole robotic glove in both active and passive modes. Preliminary experimental results showed that (1) in the active training mode, the tested human hand’s muscle effort needed to conduct gross finger flexion increased from 11.16% to 42.60% of the maximum value when the air pressure inside the minimal clutches changed from 0 kPa to 200 kPa; (2) in the passive mode, the 10-DoF robotic glove could assist the tested hand to perform various training exercises and grasp various objects with different hand postures. This paper focuses on the integrated design of multi-DoF structures and variable stiffness mechanisms, which will have an impact on the development of multifunctional soft robots and wearable devices.

The compliance of soft grippers contributes to their great superiority over rigid grippers in grasping irregularly shaped objects and forming soft contact with environments. Due to a relatively small pressure, soft grippers lack the stiffness required for wider applications. Particle jamming has been frequently reported as a means of stiffness control. Unlike previous research using vacuum for particle jamming, this paper proposes a novel passive particle jamming principle that does not need any vacuum power or other control means. The proposed method is by simply patching a silicone rubber soft actuator and a pack (made of strain-limiting membrane) of particles to form an integral gripping finger. The inflation of the soft actuator applies a pressure to the particle pack causing particles inside it to jam. A larger squeezing pressure will result in tighter particle jamming, thus increasing the stiffness of the finger. The stiffness of the finger is controllable as it is proportional to the actuator's air pressure, which has been verified by experiments in this research. The stiffness can increase more than six fold when air pressure changes from 20 to 80 kPa in the experimental studies. The reported discovery may enhance the capabilities of soft robotic grippers so that more robotic picking operations could be performed by soft grippers.

Shape memory polymer (SMP) is a type of functional materials that changes Young's modulus when heated above glass transition temperature (Tg). In this work, this property of SMP has been explored for the design and fabrication of a modular omni-directional joint with variable stiffness. When cascading a number of such joints, a variable stiffness hyper-redundant robotic arm can be built. The basic design of the variable stiffness joint is based on a ball joint where the ball is made of two materials: acrylonitrile butadiene styrene (ABS) and SMP, and the socket is made of only ABS material. When heated, the ball joint shows different resistive torques below and above the SMP's glass transition temperature Tg. Moreover, shape recovery property of SMP material above Tg guarantees the design with high repeatability. Both the ball and the socket are made by a 3D printing process fused deposition modeling (FDM). The FDM fabrication of SMP is made possible by a novel process control method in the FDM process. The ball joint's variable stiffness is tested by a number of experiments. Experimental results indicate distinct changes in resistive torques at different test temperatures. Using the proposed modular omni-directional ball joints, a variable stiffness hyper-redundant robotic arm is built.