Pareto optimization of a washing machine suspension system

The washing machine is a well known home appliance which is used at least weekly, in some cases daily, by almost every family. The importance of the task the machine performs combined with the variety of available machines has made competition between manufacturers harder and harder. Among the strongest drive forces in the field of washing machine development are the capacity increase together with reduction of energy consumption. Since the first machines with spin-drying ability the washing machine has had a reputation of being noisy and causing vibrations. A soft suspension improves the vibration isolation and reduces the vibration output, but the severity of the vibration problem can be increased with the bigger tub volume that a machine with higher capacity demands. As the same outer standard dimensions of the machine housing must be preserved, a stiffer suspension might be needed to keep the tub from hitting the housing at when passing the critical spin speed. Hence there are conflicting criterias to be dealt with.This paper focuses on several aspects of vibration dynamics in washing machines: the capacity maximization through the study of tub movement, the vibration output from the machine to the surroundings, and the “walking” tendency of the system. A computational model of a washing machine with bottom mount suspension has been built in Adams/View from MSC. Software, based on production drawings. Experimental data was used for validation of mathematical and computational models of functional components of the system as well as for the model of the complete washing machine. The models of the functional components have been parameterized and are used for suspension optimization in a computer cluster. Three objective functions related to kinematics and dynamics of washing machines have been defined and a numerical algorithm has been created to solve Pareto optimization problems. The algorithm is a genetic algorithm built around Matlab’s subroutine “gamultiobj.m” and executed on an in-house developed computer cluster with possibility of parallel computing of Adams/View models. The results are presented as optimized parameter values of suspension functional components, in this case bushings with respective Pareto fronts. The focus has been set on delivering couplings between parameter values and performance trade-offs in terms of objective functions to facilitate parameter tuning. The obtained optimization results have successively been used in the development of a novel washing machine which will go into production after the summer 2010