The fundamentals of automatic washing machine design based upon dynamic constraints
The objective of this study is to develop a fundamental resource for appliance engineers to understand the dynamic constraints involved in the design of automatic washing machines. This is accomplished through the development and examination of basic models. The fundamental characteristics of the suspension system are determined for top and bottom mount horizontal axis washers. Similitude is used to discuss the characteristics of vertical axis washers. The fundamental models developed for the suspension systems show good correlation with the dynamic response of actual washing machines. It is possible to use these fundamental models to determine limits or bounds upon the suspension stiffness of the system for both top and bottom mount suspension designs. The stability of bottom mount suspension systems is discussed. From the analysis of the suspension designs, the need for dynamic balancing of the clothes load during the spin extraction cycle is established. The need for dynamic balancing is a prominent observation of the suspension system analysis. Hence, a review of auxiliary mass damper designs is presented with emphasis on application to automatic washing machine design. Design criteria for using dynamic balancers are discussed and the limitations of these devises are explained. Liquid ring balancers show the most promise due to cost; however, mechanical balancers are more effective in controlling the system's response. Finally, a new type of dynamic balancer, the elastic mass balancer, is developed. The dynamic constraints imposed upon the washing machine design are typically tub deflection and walk performance for a given unbalanced load. The theory of walk is established using fundamental models to explore specific environmental interactions. Design criteria are developed from this analysis which will enable the washer suspension engineer to gain valuable insight into the walk response of the washing machine during the spin extraction cycle. It is shown that the spin speed achievable is dependent upon the suspension design. Without a suspension, the washing machine can only achieve spin speeds of 200 RPM while actual machines achieve spin speeds of 1600 RPM. The use of walk as a design constraint is discussed for washing machine design. Finally, the design observations for a washing machine using dynamic constraints are discussed. Through the use of these observations, a design engineer will be able to determine the benefits and limitations of a suspension design on the dynamic response of a washing machine prior to the actual development of the system. Therefore, this study gives the design engineer insights on the design of washing machine suspension systems based upon the dynamic constraints imposed upon the system by the consumer. The use of these insights should reduce the time required to develop a useful suspension system and improve the quality of the suspension design before actual construction of the product is initiated.
Soedel, Purdue University.
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