机械原理习题-机械的平衡donghuadaxue.docVIP

机械原理网络课件 机械的平衡 习题答案 概念题 1、机械平衡的目的？参考 2、什么叫静平衡？参考? ?? 什么叫动平衡？参考? ?? 各需几个平衡基面？? ?? 静平衡只需一个平衡面,而动平衡则需要两个平衡面.所以静平衡又叫Single-plane balance,而动平衡又叫two-plan balance. 3、刚性转子静平衡的力学条件是?不平衡惯性力的矢量和为零 ；动平衡的力学条件是???1)其惯性力的矢量和等于零，即∑P=0?;(2)其惯性力矩的矢量和也等于零，即∑M=0 4、图1所示的两个转子，已知m1r1=m2r2,转子(a)是 静 不平衡的；转子(b)是 动 不平衡的。 ? 图? 1???????????????? ? 5、图2(a)、(b)、(c)中，s为总质心，图? a),b)? 中的转子具有静不平衡；图? c) 中的转子具有动不平衡。 计算题 ?1、如图所示曲轴上，四个曲拐位于同一平面内，若质径积m1r1=m2r2=m3r3=m4r4,l1=l2=l3,试判断该曲轴是否符合动平衡条件？为什么？ 该曲轴符合动平衡条件 ?2、高速水泵的凸轮轴系由三个互相错开120o的偏心轮组成，每一偏心轮的质量为m,其偏心距为r,设在平衡平面A和B上个装一个平衡质量mA和mB,其回转半径为2r,其他尺寸如图所示。试求mA和mB的大小和方位（可用图解法）。 　 ??????????????????????????????????????? 题? 2 3、如图所示为一钢质圆盘。盘厚δ=20mm,在向径r1=100mm处有一直径d=50mm的通孔，向径r2=200mm处有一重量为2N的重块，为使圆盘满足静平衡条件，拟在向径r=200的圆周上再钻一通孔，试求次通孔的直径和方位（钢的重度γ=7.6×10-5N/mm3)。 ? 题? 3 4.A system of two coplanar(同一平面) arms on a common shaft, as shown in the right figure is to be designed. For the row(s) assigned in Table 1, find the shaking force of the linkage when run unbalanced at 10rad/sec and design a counterweight to statically balance the system. a mbrb=0.934 θb=-75.5o c mbrb=5.932 θb=152.3o e mbrb=7.448 θb=-80.76o 5.A wheel and tire assembly has been run at 100 rpm on a dynamic balancing machine as shown in the following figure. The force measured at the left bearing had a peak of 5 lb at a phase angle of 45o? with respect to the zero reference angle on the tire. The force measured at the right bearing had a peak of 2 lb at a phase angle of -120o with respect to the reference zero on the tire. The center distance between the two bearings on the machine is 10 in. The wheel is 7 in wide at the rim.? Calculate the size and location with respect to the tires zero reference angle, of balance weights needed on each side of the rim to dynamically balance the assembly(The whell rim diameter is 15 in). Answer:? ??? Wa=3.56lb θa=44.44o ??? Wb=2.13lb θb=-129.4o