COUPLINGS

SFS MODELDesign Check ItemsSERVO FLEXSFS• Selection procedure(1) Calculate torque Ta applied to the coupling based on themotor output P and coupling operating rotation speed n.Ta [N·m] = 9550 ×(2) Calculate corrected torque Td applied to the coupling afterdeciding the service factor K based on load conditions.Td = Ta × K (see below)P [kW]n [min −1 ]Load characterConstant Fluctuations: Slight Fluctuations: Medium Fluctuations: Large• How to evaluate the eigenfrequency offeed-screw system(1) Select the coupling according to the normal operating torqueand maximum torque of the servo motor/stepping motor. (Referto the selection procedure on the left.)(2) In the following feed-screw system, evaluate the entireeigenfrequency: Nf from the torsional stiffness: K of thecoupling and feed screw, the moment of inertia: J1 of thedriving side and the moment of inertia: J2 of the driven side.MotorCouplingFeedscrewTableBearing1.0 1.25 1.75 2.25In servo motor drive, multiply the service factor K=1.2 to 1.5 bythe maximum torque of servo motor Ts.Td = Ts × (1.2 to 1.5)(3) Select the size in order that the coupling permissible torqueTn becomes equal or greater than the corrected torque Td.Nf: Eigenfrequency of the entire feed-screw system [Hz]k: Torsional stiffness of the coupling and feed screw [N·m/rad]J1: Moment of inertia of the driving side [kg·m 2 ]J2: Moment of inertia of the driven side [kg·m 2 ]J1J2Tn ≥ Td(4) Depending on the bore diameters, the coupling permissibletorque may be limited. Refer to the “Specification” and“Standard bore diameter.”(5) Confirm if the required shaft diameter does not exceed themaximum bore diameter of the coupling.For machines whose load torques periodically fluctuatedrastically, contact us.• Feed-screw systems Oscillation phenomena of servo motorsIf the eigenfrequency of the entire feed-screw system is under400 to 500Hz, oscillation may occur depending on the gainadjustment of the servo motor. An oscillation phenomenonof a servo motor occurs mainly by the problem of theeigenfrequency of the entire feed-screw system and theelectric control system.These problems can be avoided by raising the eigenfrequencyof the mechanical system from the design phase or adjustingthe tuning function (filter function) of the servo motor. Resonance caused by stepping motorsIt is a phenomenon that occurs within a certain rotation speedrange by the pulsation frequency of the stepping motor andthe eigenfrequency of the entire system. Resonance can beavoided by not applying the resonant rotation speed, or byreviewing the eigenfrequency in the design phase.• Operating limit rotation speedFor the SFS-G long spacer type, the rotation speed at which itcan be operated differs according to the spacer length selected.Check the table below and make sure that the rotation speedto be used is lower than or equal to the operating limit rotationspeed.If the maximum rotation speed is specified by type, this specifiedrotation speed will be used as the upper limit.Operating limit rotation speed [min –1 ]300002000010000900080007000600050004000300020001000900800700600500400SFS-05GSFS-06GSFS-08GSFS-09GSFS-10GSFS-12GSFS-14GContact us for unclear points concerning ocsillation phenomenaof servo motors and resonance of stepping motors.300200200 500 1000 2000 3000Floating length [mm]38COUPLING_E_22_41new.indd 38www.feyc.es9/15/10 4:23 PM