Design and Analysis of a Novel 2T2R Parallel Mechanism with the Closed-loop Limbs

This paper presents a novel four degrees of freedom(DOF) parallel mechanism with the closed-loop limbs, which includes two translational(2 T) DOF and two rotational(2 R) DOF. By connecting the proposed parallel mechanism with the guide rail in series,the 5-DOF hybrid robot system is obtained, which can be applied for the composite material tape laying in aerospace industry. The analysis in this paper mainly focuses on the parallel module of the hybrid robot system. First, the freedom of the proposed parallel mechanism is calculated based on the screw theory. Then, according to the closed-loop vector equation, the inverse kinematics and Jacobian matrix of the parallel mechanism are carried out. Next, the workspace stiffness and dexterity analysis of the parallel mechanism are investigated based on the constraint equations, static stiffness matrix and Jacobian condition number. Finally, the correctness of the inverse kinematics and the high stiffness of the parallel mechanism are verified by the kinematics and stiffness simulation analysis, which lays a foundation for the automatic composite material tape laying.

Delayed stress memory by CaAl_(2)O_(4):Eu^(2+) mechanoluminescent phosphor with defect engineering regulation

Real-time stress sensing based on mechanoluminescence materials has been widely studied for structural health monitoring of bridges,buildings,high-pressure vessels,and other infrastructure surfaces.However,this approach is difficult to detect the stress information of closed mechanical structures.Here,we propose a delayed stress memory strategy to record the stress information of closed mechanical structure by the flexible film composed with CaAl_(2)O_(4):Eu^(2+),Sm^(3+)phosphor.After the force is applied,the optical information on the film can be read out by the near-infrared laser after a period of time without real-time monitoring,and the stress distribution information of bearings and gears in the engine can be obtained.Furthermore,the regulation of trap depth from 0.662 to 1.042 eV allows the captured carriers to remain in the traps for a long time without being released as long persistent luminescence,which is beneficial to the delayed stress memory.Therefore,this work promotes the application prospect of mechanoluminescence materials in stress sensing,and provides a new idea to record the stress information of closed mechanical structures.

An attempted approach to the tricyclic core of haliclonin A：Structural elucidation of the final product by 2D NMR

We describe the design and execution of a novel synthetic route to the tricyclic core of haliclonin A,a tetracyclic marine natural product.The approach features Bachi＇s thiol-medicated free radical cyclization of alkenyl isocyanide to build the bridged ring system,and ring-closing metathesis（RCM） reaction to form the macrocycle.Execution of the synthetic plan ultimately resulted in a diazatricyclic compound.By means of 2D NMR techniques,the structure of this compound was revealed to an unexpected product 8.Analysis of the synthetic pathways allowed concluding that the unexpected product is a result of an ＂unexpected＂ migration of olefinic bond during dioxolanation of the 2-cyclohexenone derivative 7.This investigation also resulted in a concise construction of the functionalized hexahydro-1H-isoindole-1,5（4H）-dione 12 and the macrocyclic tricyclic ring system 8.