An audio-tactile interface based on dielectric elastomer actuators

Abstract

This paper presents a concept of a dielectric elastomer actuator (DEA) user interface (smart button) that can sense a user’s touch and provide multi-sensory tactile and acoustic feedbacks through a single electrical input signal. The DEA relies on a multi-layer layout, in which a layer detects user-driven deformations (touches) via custom-built capacitance sensing electronics, and the remaining layers are used to provide actuation (audio-tactile feedbacks). Building upon a recently presented principle, combined tactile and acoustic feedbacks are produced by concurrently exciting different vibration modes of the same active membrane over different frequency ranges. An integrated demonstrator setup is presented, which includes a DEA, an acoustic enclosure, compact sensing and driving electronics. A characterization of the prototype is conducted, including an analysis of the sound pressure level, the force/stroke output at lower working frequencies, the ability to sense deformations with different profiles and produce combined audio-tactile outputs. Compared to previous works on multi-function DEAs, the system presented in this paper provides largely improved sensing performance (with lower working voltage) and features a deeper level of integration (with small-scale custom sensing electronics, and logics embedded onto scalable microcontrollers) and is thus specifically optimised for user-interaction applications. On this end, tests with users are presented here for the first time, which allowed evaluating the subjective perception of the interface’s feedbacks. By means of further optimisation and miniaturisation of the power/sensing electronics and structural components, the layout and multifunction DEA principle presented here might lead, in the future, to the development of DEA-based smart buttons for active surfaces, or portable/wearable user interfaces and communicators.

A self-sensing approach for multi-mode dielectric elastomer actuator-loudspeaker devices

“…The COP-DEA can thus work as a loudspeaker, in which sound is produced thanks to voltage-driven structural vibrations, with no significant contribution from the LF pumping mode. Because pumping and structural modes are relatively uncoupled (their passbands present little overlap, the associated deformations take place along different principal directions), different deformation modes (pumping and structural) of the COP-DEA can be exploited at the same time, with the aim of building multi-function devices [12], [13]. This can be done according to different paradigms (Figure 2).…”

“…The second term is a small-amplitude perturbation that excites the structural modes and allows generating sound. Using driving waveforms in the same form as (2), we developed DE loudspeakers able to beat the tempo of a tune through a linear motion of an end-effector [12], and user interfaces able to provide users with a combined LF vibrotactile stimulation and HF acoustic feedbacks [13].…”

“…In this case, as the linear motion of the end-effector is controlled by the user, the COP-DEA is electrically driven with a HV signal ( ) v t with constant bias (i.e., 2)) and a superimposed HF signal (e.g., a soundtrack). Combinations of the two working modes can also be envisaged, in which a COP-DEA provides vibrotactile and acoustic feedbacks (by means of a multi-harmonic excitation voltage) to users that interact with the DEA's end-effector [13].…”

“…These devices are typically driven through a high-frequency (HF) voltage signal, which induces HF vibrations of the DE that allow generating sound. In recent publications [12], [13] we showed that some DEAs, with suitable layout and control, can achieve low-frequency (LF) and HF actuation simultaneously, hence working as loudspeakers and LF linear actuators at the same time, driven by a single input voltage. Leveraging on this multifunctionality, we developed audio-tactile interfaces that can provide users with multi-sensory feedbacks using different vibration modes of a same DEA, excited by means of a multi-chromatic voltage input [13].…”

“…We focus on an actuator layout called circular out-of-plane DEA (COP-DEA) [17], which features a pumping linear actuation motion in the LF range and develops complex structural vibration modes of the DE membrane (that can be used to produce sound) at HF. In our previous studies, we demonstrated the multifunctionality of this system by making it work as a loudspeaker and a metronome (able to beat the tempo of a tune through its own pumping motion) [12] or as a user interface (audio-tactile interface) [13] driven by a high-amplitude LF voltage superimposed to a small-amplitude HF signal. Providing this system with self-sensing features would allow, among other, including advanced functionalities such as the ability to adjust the acoustic output (pitch, intensity) as a function of a user input (e.g., a touch) in acoustic interfaces, or to adaptively adjust the amplitude of the HF acoustic component as a function of the LF pumping deformation, so as to eliminate beating distortions (as observed in [12]).…”