Xu Pei

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 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.