The shape memory alloy (SMA) material is embedded into elastic material to make the bending actuator through the shrinkage property of SMA material during being heated. This production method is with the characteristics of long production time and cumbersome making process. As the SMA material is embedded in the elastic actuator, the heat dissipation with the environment is slow, resulting in low actuating efficiency. In this article, a new lightweight bending actuator is developed based on pre-bent SMA wire. The SMA wire is used as the body and actuator, and realizes the initial shape recovery through active control mode instead of relying on heat exchange only. The manufacturing process of the bending actuator is very simple and low-price. The pre-bent angle of SMA wire can be programmed to control the actuator's output angle. By modeling the phase transformation process of SMA wire, the change in Young's modulus at different temperatures is analyzed, and the actuating current and pre-bent angle of SMA wire are calculated. Based on the changing resistance of SMA wire during being heated, the strategy to avoid overheating is designed and achieved. Imitated the form of human hand grasping, a lightweight gripper with palm function is made, and four grasping strategies are designed for the gripper and tested. Finally, the gripper is tested on the continuum arm made of pre-bent actuator. The actuator broadens the application form of SMA wire actuated actuator and provides a new method for designing lightweight and miniaturized soft gripper.

In situ maintenance works for nuclear power plants are highly beneficial as they can significantly reduce the current maintenance cycle and cost. However, removing absorber balls in a constrained environment through an inspection port is fairly challenging. In this article, a 3-DOF dual-segment continuum robot system is proposed which is equipped with an end-effector to remove absorber balls by pneumatic conveying. Then, according to the symmetrical layout of actuation ropes, the kinematics of the single-segment continuum robot are extended, and the kinematics equation which is universal to the continuum robot with the dual segment is summarized. In addition, some special kinematics solutions can be obtained according to opposite-bending and feeding characteristics. Finally, the functions of the device are verified by tests. The results show that the continuum robot can smoothly pass through the divider plug and reach any position at the bottom of a ball-storage tank where absorber balls are located with only two segments. In a gas environment, the efficiency of absorber ball removal can reach 58.96 kg/h with a lift of 7.5 m and 48.54 kg/h with a lift of 10 m. This result undoubtedly paves the way for the in-service maintenance of nuclear power plants.

Compliant mechanisms, which can be integrally machined and without assembly, are well suited as joints for continuum robots (CRs), but how to incorporate the advantages of the compliant mechanism into the arm design is a key issue in this work. In this paper, a novel type of flexible spherical-hinged (FSH) joint composed of tetrahedron elements with a fixed virtual remote center of motion (RCM) at the bottom is proposed, and then extended to the CR and end-effector. In the arm design, the error compensation principle is used to offset the parasitic motion of the CR under external load (pressure and torque) and improve the bending and torsional isotropy of the arm through different series combinations, and then the stiffness model of the FSH joint and the statics model of the CR are developed using the 3D chain pseudo-rigid body model (3D-CPRBM) and tested. The results show that the 3D-CPRBM can effectively predict the deformation of the FSH joint and the CR. Moreover, the maximum standard deviation of the bending angle of the FSH joint in each direction is only 0.26 deg, the repeatable positioning accuracy of the CR can reach 0.5 deg, and the end-effector has good gripping ability and self-adaptive capability.

The transforming flexahedron origami (TFO) is a unique origami that combines the functions of fingers and palm, with a symmetrical distribution of four-finger structures and good shape adaptability. In this paper, inspired by the TFO configuration, a new type of reconfigurable gripper is designed. The kinematics and mechanics of the gripper are analyzed theoretically, and paper folding is used as the skeleton, thin film as the skin, shape memory alloy spring as the actuator, and active cooling is used to enhance the actuator efficiency. Different kinds of objects are used to test the gripping performance of the gripper, including shape adaptive ability and gripping robustness test, and the test results show that the gripper is with good gripping performance. The reconfigurable capability of the TFO configuration allows the hand gripper to have two gripping modes, adapting to the adaptive gripping of thin rod-like objects and curved objects, which is difficult to achieve with a single gripping mode. The TFO gripper provides a new way of thinking for the design of flexible and origami grippers in the future.