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《中国航空学报》2022,35(8):249-264
Currently, industrial robots are considered as an alternative towards traditional machine tools. Especially for the large-scale parts milling, robotic flexibility and low cost make it possess the irreplaceability. However, the milling chatter caused by its weak rigidity hampers robotic application and promotion severely in aviation industry. Rotary ultrasonic milling (RUM) technology with one-dimensional axial vibration has been proven and approved on avoiding robotic chatter. Based on this, the research of project team demonstrates that longitudinal-torsional composite ultrasonic milling (CUM-LT) involving separation characteristic has a greater advantage than RUM in terms of chatter suppression. Thereby, the CUM-LT as a new means is applied to avoid processing vibration of robotic milling system. And its influence mechanism on stability improvement of weak stiffness processing system is clarified. Meanwhile, the approaches to strengthen separation effect are provided innovatively. Moreover, a new analysis method of robotic CUM-LT (RCUM-LT) stability is proposed on the basis of ultrasonic function angles. The simulation and experimental results indicate that compared with robotic RUM (RRUM), stability regions of separated RCUM-LT (SRCUM-LT) and unseparated RCUM-LT (URCUM-LT) are improved by 124.42% and 39.20%, respectively. The addition of torsional ultrasonic energy has a wonderful effect on the milling chatter suppression of low stiffness robots. 相似文献
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《中国航空学报》2022,35(10):381-392
Model-based fault diagnosis serves as an efficient and powerful technique in addressing fault detection and isolation (FDI) issues for control systems. However, the standard methods and their modifications still encounter some difficulties in algorithm design and application for complex higher-order systems. To avoid these difficulties, a novel fault diagnosis framework based on multiple performance indicators of closed-loop control system is proposed. Under this framework, a so-called performance residual vector is constructed to measure the differences between the real system and the nominal model in terms of system stability, accuracy, and rapidity (SAR) respectively. The criteria for quantification, normalization of the SAR residuals and the explicit mappings between the thresholds and the required performance are given. FDI can be easily achieved simultaneously by monitoring the normalized residual vector length and direction in the SAR performance residual space. A case study on electro-hydraulic servo control system of turbofan engine is adopted to demonstrate the effectiveness of the proposed method. 相似文献
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《中国航空学报》2022,35(8):92-106
Enhancing damping characteristic is one of the effective methods to solve the instability problem of the rotor system. The three-dimensional numerical analysis model of scallop damper seal was established, and the effects of inlet pressures, preswirl ratios, rotational speeds, interlaced angles and seal cavity depths on the rotordynamic characteristics of scallop damper seal were studied based on dynamic mesh method and multi-frequencies elliptic whirling model. Results show that the direct stiffness of the scallop damper seal increases with decreasing inlet pressure and increasing rotational speed and cavity depth. When the seal cavity is interlaced by a certain angle, which shows positive direct stiffness. The effective damping of the scallop damper seal increases with the increasing inlet pressure, the decreasing preswirl ratio and the rotational speed and cavity depth. There exists an optimal interlaced angle to maximize the effective damping and the system stability. The leakage of the scallop damper seal is significantly reduced with decreasing inlet pressure. The preswirl will reduce the leakage flowrate, and the rotational speed has a slight effect on the leakage performance. The leakage of the scallop damper seal decreases with increasing seal cavity depth. 相似文献
125.
《中国航空学报》2022,35(12):144-155
To overcome the drawbacks such as large wing deformations, poor performance encountering gusts, limits in taking off and landing, inconvenience of transportation of High-Altitude Long-Endurance (HALE) Unmanned Aerial Vehicles (UAVs), a new conceptual aircraft called wingtip-docked Multi-Body Aircraft (MBA) has attracted lots of attentions. Aiming to investigate the feasibility of this concept, two UAV models were designed, manufactured and connected by a wingtip-docking mechanism, which only allows the relative roll motion between the two aircraft. The trim solution of the two connected aircraft is firstly obtained by solving the developed nonlinear flight dynamic equations, followed by the stability analysis based on the linearized model. The results show that the connected aircraft is inherently unstable and cannot fly without a reasonable flight control system. A set of Proportional-Integral-Derivative (PID) control laws was then developed and implemented in the two experimental aircraft. The success of the flight tests show that the flight control can effectively eliminate the unstable motion and the wingtip-docked MBA is controllable and feasible. 相似文献
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模糊自整定PID控制及其在航天产品真空热试验中的应用分析 总被引:2,自引:2,他引:0
文章首先分析了航天产品热试验时被控对象的特点,并进行了建模分析,接着介绍了如何通过参数自整定技术获得PID的3个初始参数,并进行了模糊自校正PID控制器设计。为了检验该控制方法的控制效果,文章选取了3次有代表性的试验数据进行了仿真分析。结果表明,模糊自校正PID控制方法具有适应性强、控制精度高、抑制试验系统温度滞后明显的优点,该方法较原控制方法超调量有所减小,过渡过程有所加快,抗干扰能力显著增强,较好地解决了控制系统快速性和小超调量之间的矛盾。 相似文献
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传统被动光钟激光锁频系统的频率稳定度最终受限于由布朗运动导致的腔长热噪声,是目前光频标发展面临的主要技术瓶颈之一。主动式新型光频标利用光学谐振腔的弱反馈在原子跃迁能级间形成多原子相干受激辐射,该受激辐射输出信号可直接作为钟跃迁信号使用,相比于被动光钟,主动光中原理上可实现更窄的量子极限线宽,并具有腔牵引抑制优势。分别介绍了国内外在主动光频标研究现状,主要介绍北京大学在该研究方向取得的理论及实验研究进展。为了实现窄线宽连续型主动光频标,提出双波长好坏腔方案减小剩余腔牵引效应对四能级主动光钟的影响,其中Nd:YAG 1 064nm好腔激光和铯原子1 470nm坏腔激光共腔输出,分别工作在好、坏腔区域,好腔激光通过Pound-Drever-Hall(PDH)稳频技术锁定主动光钟谐振腔的腔长,由于坏腔激光相比于好腔激光具有腔牵引抑制优势,因此坏腔激光线宽有望在腔长锁定之后的好腔激光的基础上进一步压窄。目前两套双波长系统的1 470nm钟激光拍频线宽受限于两个谐振腔腔长的相对抖动,为了抑制共模噪声对钟激光拍频信号的影响,并验证采用PDH稳频技术实现腔长锁定的可行性,本文利用相位锁定技术同步两套双波长好坏腔系统的谐振腔腔长,从而消除腔长共模噪声对钟激光拍频线宽的影响,进而分析除剩余腔牵引效应以外的其他因素对1 470nm主动光频标的影响。 相似文献