机械原理第六章 动平衡.pptVIP

* 第六章 机械的平衡 Chapter 6. Balancing of Machinery 1. Purposes §6-1 Introduction Dynamic press in kinematic pair Friction and inner stress in link efficiency and life-span Inertia force (torque)  Compelled oscillation The purpose of mechanical balancing is to clear up or decrease the bad effect by balancing the component’s unbalanced inertia. The balance of component rotating about a fixed axis Rotor(转子): Parts constrained to rotate about a fixed axis. 2. Contents (1)Balancing of rigid rotor刚性转子的平衡 static balancing (静平衡) dynamic balancing (动平衡) (2)Balancing of flexible rotor绕性转子的平衡 Balancing of mechanisms rigid rotor flexible rotor mechanism (avi) 1. Phenomena of static imbalance § 6-2 Calculation for static balancing of a rigid rotor If mass center of rotor doesn’t coincide with the axis of rotation, their eccentric mass will lead to centrifugal inertia force (离心力) when rotating, and causes an additional dynamic press (附加动压力)in the linkage. 2. Geometric condition  B/D ≤ 1/5 B D m3 m1 m2 m3 m1 m2 3. Theory of static balancing F1 F2 F3 m1 m2 m3 r2 r1 r3 centrifugal forces(离心力）of the unbalanced masses（偏心质量）： F1 = m1 r1w2 F2 = m2 r2w2 F3 = m3 r3w2 If , F1+F2 +F3 ≠ 0 FP mP Then , imbalance F1 F2 F3 m1 m2 m3 r2 r1 r3 F1+F2 +F3 +FP = 0 FP mP Some counterweight质量点(mp) can be added to the rotor to balance its centrifugal force . To balance: Fp = mp rpw2 m1 r1w2 + m2 r2w2 + m3 r3w2 + mP rPw2 = 0 m1 r1 + m2 r2 + m3 r3 + mP rP =0 miri ----mass-radius product (质径积) Conclusion： Requirement for static balance: ∑m1 r1=0 Add Remove Conclusion:A balance can be achieved by adding or removing a balance mass in the same plane. resolution： A. Graphical method F1 F2 F3 m1 m2 m3 r2 r1 r3 FP mP WP W1 W2 W3 Scale(比例尺)：μW = (kgm/mm) miri Wi Wi = miri m1 r1w2 + m2 r2w2 + m3 r3w2 + mP rPw2 = 0 B. Analytical method　 mx1 rx1 + mx2 rx2 + mx3 rx3 + mxP rxP = 0 my1 ry1 + my2 ry2 + my3 ry3 + myP ryP =