KMS of Xinjiang Astronomical Observatory, CAS
| 射电望远镜副反射面六自由度并联机构分析与设计 | |
| Alternative Title | Analysis and design of a 6-DOF Parallel Mechanism on the Secondary Reflector of Radio Telescope |
古丽加依娜·哈再孜汗
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| Subtype | 博士 |
| Thesis Advisor | 王娜 |
| 2021-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学博学 |
| Degree Discipline | 天文技术与方法 |
| Keyword | 并联机构 射电望远镜 副反射面 动力学 运动学 |
| Abstract | 大型射电望远镜工作过程中，主反射面、背架和副反射面支撑架等随着射电望远镜的俯仰角度的改变，存在不同程度的形变，引起主副反射面焦点偏离，造成天线效率的下降。使用调整机构对副反射面位姿进行调整，对主、副反射面焦点及馈源相心之间的误差进行实时补偿，是提高射电望远镜天线效率的有利手段，对于提高射电望远镜天线电性能具有重要的意义。使用六自由度（6-DOF）并联机构对天线副反射面位姿进行调整，充分发挥了并联机构的负载能力强、精度高、结构紧凑等优点。但以往针对并联机构所做的研究很少针对定平台姿态大范围变化的并联机构，而本文研究的6-DOF并联机构安置于射电望远镜副反射面，在对副反射面进行六自由度位姿调整的同时随射电望远镜主反射面在 0°到90°之间做俯仰运动，且负载重、精度要求高、工作条件复杂，因此为实现射电望远镜高精度定位和指向目标，本文考虑并联机构应用于射电望远镜的实际情况主要进行了如下三项研究工作： 1. 考虑电动缸丝杠装置的被动旋转及射电望远镜的俯仰运动对6-DOF并联机构建立了动力学模型。本文针对传统动力学建模方法未考虑双端虎克铰型六自由度并联机构丝杠的被动旋转，导致动力学模型得到的驱动力与实际并联机构的驱动力之间存在误差的问题，在传统方法的基础上将丝杠被动旋转作为附加运动参数进行考虑，并采用虚功原理进行综合动力学建模；进一步考虑射电望远镜俯仰运动引起的并联机构载荷变化，建立了全俯仰角下的动力学模型。最后通过数值仿真实验，分析了电动缸丝杠装置的被动旋转及射电望远镜的俯仰运动对并联机构动力学输出结果的影响。2. 建立了综合回零误差的并联机构误差模型。本文针对NSRT(Nan Shan Radio Telescope)副反射面并联机构运行一段时间后出现的指向偏差过大的情况，根据NSRT副面并联机构的结构特性及回零原理，采用矩阵微分法建立了综合回零误差的并联机构误差模型。根据建立的误差模型进行了误差仿真实验，并与实际测量得到的数据进行对比，验证了误差模型的正确性，并确定了主要误差源为回零误差。最后得出对射电望远镜这种高精度设备，以增量式编码器与限位开关相结合作为回零检测装置和反馈模块，长期工作后易造成并联机构运动精度下降。文中分析结果对NSRT的实际工程有一定的指导作用，对QTT（Qi Tai Radio Telescope）副反射面并联机构的设计分析也有一定的参考价值。3. 采用新构型的6-DOF并联机构进行了优化设计与性能分析。本文根据射电望远镜副反射面并联调整机构负载重、精度要求高、工作状态复杂且并联机构整体需要随射电望远镜主面在 0°-90° 之间俯仰运动的特点，选取了两种新构型的并联机构。为了降低射电望远镜副面6-DOF并联机构全俯仰角下的驱动力及提高负载能力，以并联机构在给定工作状态下各支腿受力峰值最小为优化目标进行了参数优化设计。对优化得到的新构型的并联机构与NSRT副反射面并联机构进行了性能对比实验，实验结果表明新构型的并联机构综合动力学及工作空间性能优于NSRT采用的传统并联机构。本文工作对QTT副反射面并联机构的方案设计提供了建议和思考。 |
| Other Abstract | During the operation of a large radio telescope, with the constant change of pitch Angle, the main reflector, the back frame and the support of the secondary reflector all have different deformations,which causes the focus deviation of the primary and secondary reflector, and leads to the poor pointing accuracy of the antenna, thus significantly reducing the working efficiency of the antenna. The adjustment mechanism of the secondary reflector is used to adjust the position and posture of the secondary reflector and compensate the errors between the focal points of the primary and secondary reflectors and the phase centers of the feeders in real time, which is a favorable means to ensure the efficient operation of the radio telescope.Therefore, it is of great significance to study the related technology of the secondary reflector adjustment mechanism for achieving high pointing accuracy of radio telescope. The six degree of freedom (6-DOF) parallel mechanism is used to adjust the postures of the antenna's secondary reflector, which gives full play to the advantages of the parallel mechanism, such as large stiffness, strong load capacity, high precision and compact structure.However, most of the previous researches on the parallel mechanism were carried out when the base platform of the parallel mechanism was in a fixed state, and the 6-DOF parallel mechanism studied in this paper is installed on the secondary reflector of the radio telescope and pitching between 0° and 90° along with the primary reflector of the radio telescope. Therefore, in order to realize the high-precision positioning and pointing of the radio telescope, the following three research works were carried out in this paper considering the actual situation of the parallel mechanism applied to the radio telescope:1. The dynamic model of the 6-UPU parallel mechanism was established considering the passive rotation of the cylinder and the pitching motion of the radio telescope. This paper considered the passive rotation of the cylinder that often neglected on traditional studies and brings the errors on the driving forces. On the basis of the traditional method, the passive rotation of the cylinder is considered as an additional motion parameter, and established dynamic model based on virtual work principle; The dynamic model of the parallel mechanism under full pitching angle was established by considering the load variation of the parallel mechanism caused by the pitching motion of the radio telescope. Finally, through numerical simulation experiments, the effects of the passive rotation of the cylinder and the pitching motion of the radio telescope on the driving forces of the parallel mechanism are analyzed.2. The error model of the parallel mechanism that considers homing error is established. This paper aims at the excessive pointing deviation of NSRT(Nan Shan Radio Telescope) after running for a period of time by the parallel mechanism, combined with the structural characteristics of the parallel mechanism and the principle of homing method, the error model was established by using matrix differential method. According to the model, the error simulation experiment is carried out, and compared the result with the actual measured data, the correctness of the error model is verified, and the main error source is determined as the homing error. Finally, it is concluded that for high-precision equipment such as radio telescopes, the combination of an incremental encoder and a limit switch is used as a zero return detection device and a feedback module, which will easily cause the movement accuracy of the parallel mechanism to decrease after long-term operation. The analysis results in this article have a certain guiding effect on the actual engineering of NSRT, and also have a certain reference value for the design and analysis of QTT (Qi Tai Radio Telescope) parallel mechanism.3. The new configuration of 6-DOF parallel mechanism has been optimized for design and performance analysis.In this paper, considering the heavy load, high accuracy requirements, complex working conditions of the parallel adjustment mechanism for the secondary reflecting surface of the radio telescope, and the overall need for the parallel mechanism to move with the primary reflector of the radio telescope between 0°-90°, two new types of parallel mechanisms were selected in this paper. In order to reduce the driving force and improve the load capacity of the 6-DOF parallel mechanism under the full pitch Angle of the radio telescope, the parameter optimization design was carried out with the objective of minimizing the stress peak of each leg of the parallel mechanism under the given working state. The performance of the new parallel mechanism was compared with that of NSRT. The experimental results show that the comprehensive dynamics and workspace performance of the new parallel mechanism is better than that of the traditional parallel mechanism used by NSRT. The work in this paper provides suggestions and considerations for the design of the parallel mechanism with the QTT . |
| Pages | 86 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4737 |
| Collection | 研究生学位论文 射电天文研究室 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 古丽加依娜·哈再孜汗. 射电望远镜副反射面六自由度并联机构分析与设计[D]. 北京. 中国科学院大学,2021. |
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