321 #BMM 4DSFX 4FMFDUJPO 1SPDFEVSF Basic ball screw selection procedure and required evaluation items are shown below. %FUFSNJOF UIF BQQMJDBUJPO QBSBNFUFST *OUFSJN TFMFDUJPO PG CBMM TDSFX TQFDJGJDBUJPOT &WBMVBUJPO PG WBSJPVT CBTJD TBGFUZ GBDUPST &WBMVBUJPOT CBTFE PO SFRVJSFE QFSGPSNBODFT Moving mass, feed speed, motion pattern, screw shaft rotational speed, stroke, mounting orientation (horizontal or vertical), life, positioning accuracy Temporary selection of ball screw lead accuracy grade (C3~C10), shaft diameter, lead, and length. P.321 , 322 tAxial Load Capacity Confirm that the applied axial load is within the ball screw's axial load capacity rating. P.323 tAllowable Rotational Speed Confirm that the intended shaft rotational speed is within the ball screw's allowable rotational speed rating. P.324 t Life Confirm that the ball screw satisfies the life requirement. P.325 If higher positioning accuracy and/or improved responsiveness is needed, below parameters need to be evaluated. tScrew shaft rigidity P.326 tEffects of temperature variation on life P.326 #BMM 4DSFX -FBE "DDVSBDZ Ball screw lead accuracy is defined by JIS Standards property parameters (ep, vu, v300, v2π). Parameter definitions and allowable values are shown below. In general, a ball screw lead accuracy grade is selected by evaluating if the Actual Mean Travel Error of a candidate is within the allowable positioning error. Effective Thread Length ( lu ) Actual Travel ( la ) Line Actual Mean Travel ( lm ) Line Specified Travel ( ls ) Line Nominal Travel ( lo ) Line 300mm 2π + − 0’ 0 Travel Error è2V 300 V uV ep t /( /( 5FSNT 4ZNCPMT .FBOJOH "DUVBM .FBO 5SBWFM &SSPS A value that is Specified Travel subtracted from Actual Mean Travel. 7BSJBUJPO 300 2π The maximum difference of the actual travel contained between two lines drawn parallel to the actual mean travel, and is defined by three parameters below. Variation for the effective thread length of screw shaft. Variation for an arbitrarily taken length of 300mm within the effective thread length of screw shaft. Variation for an arbitrary one revolution (2πrad) taken within the effective thread length of screw shaft. 4QFDJGJFE 5SBWFM Axial travel compensated for temperature rise and loading conditions, in relation to the Nominal Travel (Lead). 4QFDJGJFE 5SBWFM 5BSHFU 7BMVF A value that is Nominal Travel subtracted from Specified Travel, over the effective thread length. This value is set to compensate for possible screw shaft expansion and contraction due to temperature changes and applied loads. The value is to be determined based on experiments or experiences. "DUVBM 5SBWFM Actually measured travel distance "DUVBM .FBO 5SBWFM A straight line representing the actual travel trend. A straight line obtained by the least-squares method or other approximation methods from the curve representing the actual travel. Q5BCMF 1PTJUJPOJOH 4DSFX $ $MBTT "DUVBM .FBO 5SBWFM &SSPS FQ BOE 7BSJBUJPO 7V BMMPXBODFT Unit : μm 5ISFBE &GGFDUJWF -FOHUI NN "DDVSBDZ (SBEF $ $ PWFS PS MFTT "DUVBM .FBO 5SBWFM &SSPS 7BSJBUJPO "DUVBM .FBO 5SBWFM &SSPS 7BSJBUJPO 315 400 500 630 800 1000 1250 315 400 500 630 800 1000 1250 1600 12 13 15 16 18 21 24 29 8 10 10 12 13 15 16 18 23 25 27 30 35 40 46 54 18 20 20 23 25 27 30 35 Q5BCMF 1PTJUJPOJOH 4DSFXT $ $MBTT WBSJBUJPO QFS NN 7BSJBUJPO QFS SPUBUJPO è TUBOEBSE WBMVFT Unit : μm "DDVSBDZ (SBEF $ $ Parameters V300 V2π V300 V2π Standard Values 8 6 18 8 Q5BCMF 5SBOTGFS 4DSFX $U $MBTT WBSJBUJPO QFS NN 7 4UBOEBSET Unit : μm "DDVSBDZ (SBEF $U $U V300 52 210 &Actual Mean Travel Error (ep) for Transfer Screws (Ct Class) is calculated as ep=2·Lu/300·V300 Ball Screws Selection of Ball Screws 1
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