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Tham khảo tài liệu 'sổ tay tiêu chuẩn thiết kế máy p24', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 20 POWER SCREWS Rudolph J. Eggert Ph.D. P.E. Associate Professor of Mechanical Engineering University of Idaho Boise Idaho 20.1 INTRODUCTION 20.2 20.2 KINEMATICS 20.3 20.3 MECHANICS 20.6 20.4 BUCKLING AND DEFLECTION 20.8 20.5 STRESSES 20.9 20.6 BALL SCREWS 20.10 20.7 OTHER DESIGN CONSIDERATIONS 20.12 REFERENCES 20.13 LIST OF SYMBOLS A Area A t Screw translation acceleration C End condition constant d Major diameter dc Collar diameter dm Mean diameter dr Root or minor diameter E Modulus of elasticity F Load force Fc Critical load force G Shear modulus h Height of engaged threads I Second moment of area J Polar second moment of area k Radius of gyration L Thread lead Lc Column length n Angular speed r min ns Number of thread starts 20.1 20.2 STANDARD HANDBOOK OF MACHINE DESIGN Ne Pi P Sy Tc Ti tr tl t V t w Number of engaged threads Basic load rating Thread pitch Yield strength Collar friction torque Basic static thrust capacity Raising torque Lowering torque Time Screw translation speed Thread width at root W Input work Wo Output work a Flank angle a Normalized flank angle p Thread geometry parameter Ax Screw translation A0 Screw rotation I Efficiency X Lead angle p Coefficient of thread friction pc Coefficient of collar friction o Normal stress o von Mises stress t Shear stress P Helix angle 20.1 INTRODUCTION Power screws convert the input rotation of an applied torque to the output translation of an axial force. They find use in machines such as universal tensile testing machines machine tools automotive jacks vises aircraft flap extenders trench braces linear actuators adjustable floor posts micrometers and C-clamps. The mechanical advantage inherent in the screw is exploited to produce large axial forces in response to small torques. Typical design considerations discussed in the following sections include kinematics mechanics buckling and deflection and stresses. Two principal categories of power screws are machine screws and recirculatingball screws. .
