The Design And Manufacture Of A New Measuring Instrument For Curve Surface

Measuring complicated curve surface have been a hot spot in developedcountries for long time. Many states have invested much manpower, materialresources in the field and have obtained breakthrough. My tutor ProfessorSong Yuquan proposed design scheme of measuring instrument fornon-sphere surface in 1996 and gained practical new-style patent. Its basicprinciple formulae were listed as following:In practical engineering application he also brought forward alterablewidth measurement of chord height for spherical metrical head. It couldachieve random adjustment of width and eliminate measuring error producedfrom measuring feet abrasion. This paper based on the principle and designeda suit of measuring instrument for non-sphere curve surface. Compared tothree-coordinates in existence used for measuring curve surface, it had theadvantage of simple structure, convenient operation and costed less. What'smore, it had no special requirements of circumstances which meant that itcould be not only fixed immovably to measure big curve surface but alsotaken to manufactory scene for measuring protruding and concave surface ofmiddle and small type of parts. In this paper three design schemes were listed: fixed width measurementof chord height structure, alterable width measurement of chord heightstructure, alterable width measurement of chord height for spherical metricalhead structure. We summarized shortcomings of the first two schemes andput forwarded the third scheme: to satisfy condition needed for measuring hand ?h, (1)we adopted gear type framework so as to realize synchronouscircumrotation movement. The axis of the two joggled gears was fixed on theconnected rack, then left and right measuring poles were linked to gearswhose center lines passed axes of gears, so distance between center lines thetwo measuring poles could be assured. (2)To satisfy condition we linked theupper end of middle pole to raster displacement sensor with high precisiondirectly. (3) As a result of measuring parts with different sizes we designeddifferent length prolonged poles for convenient operation. They wererevolved in left, middle and right poles, so they would be replaced randomlywhen parts have different requirements for length of measuring feet. Synchronous circumrotation framework was considered emphaticallywhen we designed measuring instrument for curve surface. As its precisionhad great influence on final measuring precision, at last we introducedjoggled gears to ensure synchronous circumrotation of the two measuringfeet based on analysis of prevenient schemes. Circumrotation framework ofmeasuring instrument for curve surface had small power, high precision andstrict requirements for delay return. Gears with improved precision couldhelp to minish the delay, but it was nearly impossible to manufacture gearswith no error. Then we made some improvements in the structure to controland eliminate clearance. Since backlash of the tooth profiles existed in gears,delay return in gear framework was induced when gears start backspin. Weemployed two gears which had certain dislocation along circle girth andmotion restricted along axis aspect, so the instrument avoided the influenceof backlash of the tooth profiles completely and achieved excellenttransmission by gears with usual precision.