Development Of Indoor 80m Large-scale Laser Comparator National Standard

An 80m large-scale laser comparator national startand is invented to meet the urgent needs from the advanced manufacturing,precision engineering and other fields which demand for large-scale metrology and its traceability system.The 80m comparator is innovatively designed based on other comparators,and following three measurement principles of precise,large range and wide adaptation.The design details of each subsystem are elaborated,including a laser length measuring system composed by 3 laser interferometers,a long rail with air flotation support system and precision adjustment system,an air refractive index real-time compensated system,an automatic control air-floating platform with high precise,an image aiming system,and other auxiliary equipment such as non-Abbe-error length measuring machine,and a self-developed software control system.To eliminate the Abbe error in large-scale length measurement,an algorithm which based on three independent laser interferometers is proposed,the mounting positions of three interferometers can be arranged in any triangle.By constructing a virtual interferometer which common path with the calibrated instrument,then the length measuring formula is derived.To verify the effectiveness of the algorithm,by changing the mounting position of the calibrated instrument,different experiments are carried out within long range.The results indicate that the proposed algorithm can eliminate the Abbe error effectively.To solve the problem of air refractive index accurate correction in large-scale measurement,the existing refractive correction models are introduced,the correction models of air pressure,air humidity and temperature are given respectively.And the correction uncertainty of each influencing factor is detailed analyzed.To fully investigate the comparator performance,the tests of long-term stability of the long rail,the positioning accuracy of air flotation platform and the compensation accuracy of air refractive index are carried out.The results indicate that the straightness of the upper rail surface is less than 400μm/80m,the straightness of the side guide surface is less than 400μm/80m;the closed-loop control positioning accuracy of the air flotation platform is better than 1μm;the standard uncertainty of refractive index correction is better than 2.0×10^-8 L.Then the uncertainty of the comparator is systematically modeled,and the uncertainties introduced by the laser wavelength stability and other components are detailed analyzed.The uncertainties of the comparator measuring high-precision instruments and other different situations are given.The technical indexes of the comparator reach the domestic leading position and international advanced level.The comparator has been built as national large-scale standard in 2014,and become the headstream of domestic large-scale value traceability chain.The comparator has held 8 new calibration items.Besides,2 new national calibration specifications have also been published.At present,this comparator is the top large-scale standard equipment in China with the largest measuring range,the highest precision,the most comprehensive functions and the highest level of automation.The comparator provides the large-scale value transfer for provincial metrology institutes,troops and other institutes.It also provides the traceability standards for large-scale measuring instruments such as laser interferometers,and artefacts such as standard ball bars.The comparator further satisfies the demand for domestic large-scale metrology,and has been applied as demonstration in domestic metrology system,troops and many other fields,which has created huge social and economic benefits.