Application of the Magic Formula for Dynamic Modeling of Friction Dampers used in Drum-Type Washing Machines

摘要

In a washing machine, the highest vibration and noise occurs in a dehydration process. To reduce the vibration in washing machines, several types of dampers had been developed and used. A friction damper had been widely used for its cheap cost, which is composed of an inner tube, an outer tube, and a rubber sponge between two tubes. The lubrication state in sponge and the clearance between two tubes mainly control damping ratio, and the rubber sponge is pasted with grease to reduce friction and wear. Once the inner tube is forced to move due to vibration of the drum, then a friction force occurs. In this case, the induced friction force activates a visco-elastic deformation of the rubber sponge, in which a stick-slip motion occurs. In some dampers, there is a free-stroke region not to invoke high frictional force in a small displacement region. In this paper, physical tests for dampers were first carried out to determine the characteristics of the damper by changing excitation amplitudes and frequencies. Then, a mathematical model of a friction damper is derived, and the Magic formula model was suggested to express the experimental result. Optimum values of parameters in the Magic formula model were evaluated through an optimization technique, and the results with Magic formula model were compared to other models.