为研究波轮式全自动洗衣机脱水振动特性，首先将非线性模型在静平衡点处线性化，用雅可比矩阵作为刚度矩阵，进行模态分析。分析了刚度矩阵的构成，并给出了其表达式。在模态分析的基础上，指出了洗衣机中的摆动振型，并分析了其影响因素。通过数值仿真，分析了摆动振型随吊杆切向阻尼的变化，讨论了脱水过程中的摆动平衡区与转子平衡区，进而分析了临界阻尼的存在性及其影响因素。采用二分法求取某型号洗衣机的临界阻尼点，经过计算点的拟和，指出了临界阻尼与衣物偏心距间存在近似的二次函数关系。通过实验，验证了临界阻尼的存在。最后在本文结论的基础上，分析了液体平衡环的作用。

This paper details pendulum characteristic linked with a vertical automatic washing machine. At first, a non-linear mode provided in [2] is linearized at its static equilibrium position and ingredients of its Jacobian matrix are analyzed. Second, the pendulum mode born with the machine is obtained by an eigensolution, and factors contribute to this mode are discussed. Third, relationships between the pendulum mode and a damp coefficient in the suspenders are found based on simulation results and pendulum characteristics are analyzed. The existence of the critical damp coefficient is discussed based on energy, factors affect it are then considered. Fourth, the bisection method is employed to determine the critical damp coefficient in a particular washing machine; relationships between the damp coefficient and radius of unbalance under different rotation speed are then fitted by several second order polynomials. The existence of the critical damp coefficient is supported through experiment and effect of the hydraulic balancer is finally discussed.