30 m口径望远镜(TMT)的三镜跟踪系统(M3PA)的运动性能和指向精度指标均高于已建成的各大望远镜，且工况复杂多变，给设计人员带来了巨大的挑战。三镜跟踪系统包括Rotator轴和Tilt 轴两部分。重点研究了Tilt轴轴承布置方案以及相应分析。提出了两种轴承方案，经过分析，使用一对双列角接触转盘轴承的方案更适合于Tilt轴的工作需要，此时结构第一阶谐振频率可达到15.1 Hz，满足Tilt轴的设计要求。选定方案后，针对所选择的轴承，使用ANSYS进行了仿真。仿真结果显示，所选轴承中滚动体的最大承载达到5 000 N，最大应力大约为2 300 MPa，承载曲线满足经典余弦分布，从而证明仿真数据可靠，模拟方法可信；另外四列滚动体上都有明显的承载，从而说明所选择的轴系能够很好地将载荷分散到两侧结构架上。分析结果表明，这种结构形式能够满足TMT三镜系统对刚度要求。

The tertiary mirror pointing assembly(M3PA) of the thirty meters telescope(TMT) is the largest tertiary mirror in the world. The tracking and pointing performance of M3PA is better than any other telescopes which have been built, and the working condition is even worse. So the designers face an enormous challenge. The tracking system includes the bottom rotator axes and the tilt axes. The study of this paper focused on the tilt axes. There were two bearing arrangement methods for the tilt axes. The first one used two single angular contact bearing to stand the shaft. The second used two double rows angular contact bearings. They both met the requirement when the M3PA was vertical. But the first method became invalid when the M3PA was horizontal, while the second can provide a better support about 15.1 Hz of the first modal frequency. Then some FEA were done to find out the carrying capacity of the bearings. The results show that the maximum load applied on the rollers is up to 5 000 N, while the maximum stress is up to 2 300 MPa. Otherwise, the load distribution just likes a cosine curve. So it can be found that the analysis is believable. In addition, there are evident load applied on the four rows rollers, which proves that the bearing arrangement can disperse the load effectively. It can be concluded that the selection of the bearing arrangement is a good choice for TMT tilt axes design.