The dynamic modeling and design improvement of a piezoelectric exciter of a touch screen device for efficient tactile feedback

Abstract

Piezoelectric exciters have been receiving greater attention recently as a vibration source for tactile feedback in devices with touch screens, such as a mobile phones, in place of DC motors due to lower energy consumption and smaller volume. Their insufficient excitation level, however, still remains a problem. In this paper, dynamic modeling and design improvement of a piezoelectric exciter are presented. The excitation performance is defined as the acceleration response at the center of a touch screen per electric power and to be maximized around 250 Hz where the index finger is most sensitive. The piezoelectric exciter consists of a z-shaped metal beam, a piezoelectric layer on the long horizontal segment and an adhesive layer between the short horizontal segment and the touch screen. Assuming that the piezoelectric exciter is attached onto a rigid ground due to its low mechanical impedance compared with that of the touch screen, the piezoelectric exciter is dynamically modeled by applying Hamilton's principle, where the adhesive layer is treated as a distributed stiffness. The touch screen is modeled approximately as a simply supported beam such that it may have the same fundamental natural frequency and bending stiffness as the screen based on measurements. The performance improvement is focused on the change of five geometric parameters of the piezoelectric exciter: length of the long horizontal segment, thickness of the piezoelectric layer, thickness of the elastic metal layer, width of the beams and tip mass. The procedure to improve the performance of the piezoelectric exciter via dynamic modeling is presented together with experimental results on a prototype. Effectiveness of the design modification and limitations in practice are further discussed as well.