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Traction robot conveying technology is efficient in horizontal well logging. Auto-centralizer is an assistant support to bear the weight of robot and center the robot in casing while logging. The mechanical model for an auto-centralizer with four pair of bias arms was built based on spring-lever mechanism. ADAMS (Automatic Dynamic Analysis of Mechanical Systems) was applied to analyze the sensitiveness coefficient of structural parameters and spring force, thus optimizing the structural parameters. Consequently, a simulation model was built based on the optimization result, and a simulation study was carried out on the mechanical properties and dynamic performance with the ADAMS mechanics system modeling and simulation module. The results implied that the original structure had a disadvantage while traversing obstacles. Further studies indicated that the coupling between the pair arms adopted hinge joint, which couldn't form a closed triangle of force while traversing obstacles. We have employed an improved structure by adding a connecting lever to eliminate the constraint between the arms. Contrast experiments show that the new structure avoids bearing the load with one side and has less shock while traversing obstacles, thus improving smoothness of movement for the traction robot. 摘要: 牵引机器人输送技术是油田水平井测试中仪器输送的有效手段, 自动定心机构是牵引机器人的辅助支撑, 用来承受牵引机器人的自重, 使机器人始终保持与管道同轴。通过对弹簧蓄能轮式定心机构结构形式与工作原理的研究, 建立了偏置式4对臂自动定心机构的力学模型; 利用ADAMS (Automatic Dynamic Analysis of Mechanical Systems)的优化工具, 分析了各结构参数与弹簧力的敏感系数, 完成了结构参数的优化; 根据优化结果建立了仿真模型, 利用ADAMS的机械系统建模与仿真模块对其力学特性及动态性能进行了仿真研究, 发现越障时结构上存在缺陷, 由于两臂之间采用铰接, 越障时不能形成独立的力封闭三角形。据此提出了改进方案, 通过增加连杆来消除两臂间的制约关系。改进后的模型在越障时避免了单侧轮受力, 减少了冲击, 提高了机器人运动的平稳性。 Key words: horizontal well, traction robot, auto-centralizer, dynamic simulation