Experiencing coupled resonance dynamics when designing with vibrotactile actuators

Vibrotactile actuators are used in touchscreens to create tactile feedback and defined crispy surface dynamics. Being mounted on such plastic structures the resulting surface dynamics can differ substantially from what idle actuator specifications predict. This paper identifies the root cause as a coupled resonance interaction between the actuator’s internal spring-mass-damper-system and the structural modes of the systems, and demonstrates that this interaction is very predictable from two standard measurements performed on the actuator alone. As a representative setting five rectangular polycarbonate plates of varying thickness are studied under three conditions: bare plate, bare plate with mounted actuator as a bare mass, and actuator with free moving mass. Laser Doppler vibrometer measurements show that when the plate’s natural frequency approaches the actuator’s internal resonance, the free actuator acts as a dynamic vibration absorber (DVA), splitting the structural resonance and introducing a pronounced anti-resonance. A Rayleigh-Ritz plate model coupled to a lumped-parameter actuator model parameterised exclusively by idle and blocked test measurements predicts all three response conditions without any fitting to plate data. The results establish internal mechanical impedance as the missing design parameter in vibrotactile system integration, and motivate a standardised two-test characterisation methodology applicable across many actuator types.

Subjects

vibrotactile actuators

dynamic vibration absorber

coupled resonance

mechanical impedance

lumped-parameter model

structural dynamics

haptic system design

DDC Class

620: Engineering

Funding(s)

Laboratorien für Innovationen und Gesellschaftliche Entwicklung durch den Transfer von Ideen

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Experiencing coupled resonance dynamics when designing with vibrotactile actuators