By 2013, there will be four major cities in the worldGlobal Navigation Satellite System, except for those already in mature commercial operation in the United StatesGPSOutside the system, China'sBeidou systemEuropeanGalileo system, RussianGLONASS systemThey are still under construction.“Galileo satellite navigation project ”The original idea was to form a network of 30 satellites to compete with the global positioning system of the United States. At the beginning of the design, it was proposed that the system should be officially put into operation in 2008, and then postponed to 2014. Only four satellites in the whole system were in orbit (up to 2012). In fact, it is mainly used to further verify the system designdesign schemeandWorking systemAfter that, Galileo's official satellite will start to launch.The official networking satellite is being prepared.Chinasatellite navigation system Senior Engineer of Management OfficeYang QiangwenIntroduction: Until 2012, the satellites in orbit of "Galileo System" were only verification satellites[1]。
dispute
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As early as 2002, due to the leadership of Germany and ItalyESAThe dispute over the implementation of the Galileo Satellite Navigation Plan has led to the failure of half of ESA's budget.Among the reasons for Galileo's repeated postponement of this plan are economic factors. Europe is facing an economic crisis.Some time before the economic crisis, Europeans did have many different opinions on Galileo's investment, with some ups and downs.Another reason for the delay of the Galileo Plan lies in the political system of the EU, which also delays its progress due to the need for long consultations among many countries.Compared with Galileo system, China is also under constructionBeidou navigation systemIt is progressing smoothly and has started to provide trial operation services of continuous navigation, positioning and time service to China and surrounding areas[2]。
Positioning accuracy in mechanical manufacturing
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In mechanical manufacturing, it refers to the gap between the actual position of parts or tools and the standard position (theoretical position, ideal position). The smaller the gap, the higher the precision.It is the premise of ensuring the machining accuracy of parts.Precision machinery requires very high precision, and any slight difference will cause serious consequences.The unit of precision is very small, usually in microns[1]。
Machine tool positioning accuracy inspection
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numerical control machineIts positioning accuracy has its special significance.It indicates that the measured moving parts of the machine toolNumerical control deviceThe accuracy that can be achieved under control.Therefore, according to the measured one digit accuracy value, the best workpiece processing accuracy that this machine tool can achieve in the future automatic processing can be judged.
The main inspection contents of positioning accuracy include:
① Linear motion positioning accuracy (including X, Y, Z, U, V, W axes);
③ Return precision of mechanical origin of linear motion axis;
④ Measurement of linear motion loss;
⑤ Positioning accuracy of rotary motion (turntable axis a, b, c);
⑥ Repeated positioning accuracy of rotary motion;
⑦ Return precision of the origin of rotation;
⑧ Measurement of loss of momentum of rotation axis movement.
Testing tools for measuring linear motion include micrometer and group gauge, standard length scale and opticsReading microscopeandDual frequency laser interferometerEtc.The standard length measurement is subject to the dual frequency laser interferometer.
Rotating motion detection tools include: 360 tooth precision indexing standard turntable or angle polyhedron, high-precision circular grating andCollimatoretc.[3]。
