| Minimally Invasive Surgery(MIS) is a hot research area in the medical field, with its broad adaptability and minimally-invasive performance, high safety, quick recovery after operation and other advantages, having gained wide attention in recent years. Medical robotics facing this field has also been a rapid development. In order to simulate the complex operation which doctors make in the surgery, a variety of mechanisms with the function of remote center of motion(RCM) have emerged at the right time. This paper classifies and concludes remote center of motion mechanisms which are more successful currently, combined with their advantages and disadvantages, taking into account the big rigidity of parallel mechanism, high precision, good bearing capacity, compact structure and other advantages. A remote center of motion program realized by parallel mechanism is proposed in this paper.Through analysis and comparison, the number and spatial location of kinematic pairs of the mechanism can be determined, and the UPR-2UPRR mechanism is chosen as the research object to carry out research which is relevant to parallel mechanisms with remote center of motion. The UPR-2UPRR mechanism is divided into three sub-assemblies, which are base and U joint sub-assembly, telescopic link assembly and swing arm assembly. Coordinating relationship between each sub-assembly, detailed design for each part is given in this paper. According to the functions to be realized by each sub-assembly, a variety of methods for each sub-assembly are proposed. Considering the stiffness, strength, accuracy and reasonableness of the process, the final design of mechanism is determined. The three-dimensional model of the UPR-2UPRR mechanism is built, engineering drawings are also available, the process and assemble of the prototype is completed.Through the analysis of the UPR-2UPRR mechanism structure, equivalent relationship between vectors within the movement branched plane is established, and inverse kinematics of the mechanism is solved. By combining the method of exhaustion based on inverse kinematics of the mechanism, the work space is computed. Solving the first derivative of time for displacement vectors within a single movement branch, the Jacobean matrix of the mechanism is available. Hence, global performance evaluation of the mechanism is established which is used as the objective function to optimize the structural design. Selecting the size of key structure as the optimization objective, structure sizes can be determined according to the optimization design based on Particle Swarm Optimization(PSO).The first order influence coefficient of a single movement branch and the mechanism is deduced. By the first order influence coefficient combining principle of virtual work, the linear mapping relationship between driving forces on telescopic links and operating forces at the end of the surgical instrument can be computed. The driving forces of mechanism by analyzing and calculating using the first order influence coefficient. And the simulation analysis on the virtual prototype is completed in Adams circumstance to test and verify the rationality of theoretical derivation. Taking into account the safety and reliability of mechanism movement, the strength of key parts of the mechanism is checked to ensure the movement function of mechanism can be realized.According to the prototype of UPR-2UPRR mechanism, the electrical control equipment is constructed, including servo motors, actuators, the upper computer and other components to be a closed-loop control. The above-mentioned components form a whole mechanical and electrical control system. Homologous upper computer software is written, and the movement functional confirmatory experiment of the mechanism is finished to confirm the validity of mechanism configuration. What is more, the experiments on point to point control of the mechanism and on track movement are designed to analyze movement performance of mechanism. |
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