Daniel C. Conrad

Active control of vibrations of a metal panel by means of piezoelectric actuators and sensors

Vibration control of flexible structures composed by plates and shells became a serious problem in the last decade. In this paper the noise problem of modern washers is analyzed and a general investigation on the use of thin in-plane piezoelectric actuators and sensors to accomplish active vibration suppression in the lateral panel of an horizontal axis washing machine is performed. Experimental modal identification and validation of a finite element model of the panel is performed. Very high modal density and very low damping and close zero-pole pairs in proximity of each resonance are displayed, making control not an easy task. A digital control strategy is applied in view of a future general application to mass production home-appliance industry taking into consideration the real excitation conditions of a washing machine. The paper describes the experimental apparatus and real-time procedures implemented and discusses results.

Investigation of passive and adaptive passive dynamic absorbers applied to an automatic washer suspension design

Alternative vibration control systems are of interest to the appliance industry to improve the performance of the automatic washer suspension. Consumer benefits from improved suspension performance include noise and vibration reduction, lighter machines and larger baskets for increased clothes load capacity. Passive dynamic absorbers are investigated because of their ability to control system resonances and absorb energy from vibrating components. Since the suspended mass is variable due to different clothes loads and the amount of water in the clothes, performance limitations exist for the passive vibration absorber. Adaptive passive dynamic absorbers are investigated as an alternative vibration control system. A set of design variables and constraints for a fundamental model of an automatic washer suspension incorporating both passive and adaptive passive dynamic absorbers is presented. Numerical integration is used to obtain each system response. Optimization of the fundamental automatic washer model incorporating a passive dynamic absorber is performed. Design of experiment techniques and general design studies are used to gain information concerning the importance of the design variables on the performance of the adaptive passive dynamic absorber. Both ideal and real absorber stiffness controller schemes are investigated. The results suggest some benefit of applying adaptive passive dynamic absorbers. Design constraints are found to play a major role in the feasibility of application of this technology to the appliance industry. When considering design cost and performance, the optimum passive dynamic absorber is shown to be the better choice. Examples of various methods of implementation of both passive and adaptive passive dynamic absorbers to an automatic washer are presented.