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Topology optimization is a widely used lightweight design method for structural design of the collaborative robot. In this article, a topology optimization method for the robot lightweight design is proposed based on finite element analysis of the assembly so as to get the minimized weight and to avoid the stress analysis distortion phenomenon that compared the conventional topology optimization method by adding equivalent confining forces at the analyzed part’s boundary. For this method, the stress and deformation of the robot’s parts are calculated based on the finite element analysis of the assembly model. Then, the structure of the parts is redesigned with the goal of minimized mass and the constraint of maximum displacement of the robot’s end by topology optimization. The proposed method has the advantages of a better lightweight effect compared with the conventional one, which is demonstrated by a simple two-linkage robot lightweight design. Finally, the method is applied on a 5 degree of freedom upper-limb exoskeleton robot for lightweight design. Results show that there is a 10.4% reduction of the mass compared with the conventional method.

Physical human-robot interaction(pHRI) is the most popular way to ensure the safety in robot surgery. Current research of pHRI in operation room focuses on the inside of the surgical area, which adapts virtual fixtures method for ensuring the safety of drag. But the safety problems caused by human error in the stage of dragging the robot from the outside surgical area to the inside surgical area are ignored. Therefore, a method of applying virtual fixtures to the outside of the surgical area is proposed to solve the safety issues during dragging stage outside surgical area. This method takes the kinematics model of human arm as the reference motion trajectory to construct the guided virtual fixtures, which is to restrict the robot movement in a defined area during the pHRI drag. This drag is based on admittance control method to improve safety and ensure flexibility. Experiment results show that the constructed guided virtual fixtures with the trajectory of the human arm model as the central axis, with radius 30mm, and restrict area 5mm can effectively limit the robot motion to a certain range. Simultaneously, the output speed of the robot in tangent direction of the central axis can well follow the change of the force applied by the doctor, and the output speed in the normal direction of the central axis can converge to zero stably at the pipeline boundary. Consequently, the purpose of improving the safety and flexibility of the surgical robot before surgical operation is realized. INDEX TERMS Physical human-robot interaction, security control strategy, arm kinematics, virtual fixtures, surgical robot.

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