As touchscreen interfaces become increasingly prevalent in automobile applications, the visual overload of information poses significant safety concerns. Haptic feedback technology has emerged as a potential solution to improve user experience and minimize cognitive strain while interacting with touchscreens. hap2U's haptic technology, recently acquired by Vibra Nova, relies on ultrasonic wave propagation created by piezoelectric actuators to address this challenge.
The technology works by reducing the friction coefficient between the user's finger and the glass surface of the haptic display. This phenomenon, known as active lubrication, is achieved through the vibration produced by the actuators. Ultrasonic vibration reduces the contact area of a fingertip, thereby lowering its coefficient of friction. By controlling the contact with the plate surface through the activation and deactivation of ultrasonic vibration, compelling tactile sensations can be realized.
To optimize the system's excitation and simplify the instruction, a global resonance of the display is utilized. Laser Doppler vibrometry, employed by Polytec, plays a crucial role in assessing the mechanical performance of the system by measuring the vibration amplitude at the plate's surface. For automotive applications, it is essential to characterize the propagation of ultrasonic waves throughout the temperature range of -40 to 85 °C, ensuring reliable performance under various conditions.
The displays currently in use are multi-layer mechanical systems, comprising numerous plastic and adhesive compounds with mechanical properties that vary with temperature. As hap2U/Vibra Nova operates in the ultrasonic frequency region, data on the properties of such materials is scarce in the literature. Consequently, hap2U/Vibra Nova has developed the expertise necessary to characterize these systems at various ultrasonic frequencies and temperatures.
To achieve this, the system is subjected to varying temperatures within a climatic chamber, and a Polytec 3D Scanning Vibrometer measures the vibrations produced on the entire surface of the display. The Polytec Laser can monitor very small vibrations in the subnanometer range, even through a glass or plexiglass wall. The activation of piezoelectric elements causes ultrasonic vibration, resulting in a flexural wave in the display, which is monitored to obtain vibrational maps.
The acoustic properties of the display are assessed at various temperatures to determine if the system behavior is suitable for wave propagation. One of the most critical parameters to consider is the display's damping, characterized by the attenuation coefficient. This coefficient is determined by generating an impulse using a piezoelectric element on the display's surface and detecting the resulting displacement using a laser vibrometer throughout the sample's surface.
Comparative studies of different displays at various temperatures reveal that displays with lower damping and minimal variation with temperature and excitation frequency provide the best performance for haptic compatibility in automotive applications. Scanning laser vibrometry proves to be an effective approach for characterizing the acoustic and damping properties of haptic displays across temperature and frequency, ensuring optimal performance throughout the wide temperature range required by automotive specifications.
As the demand for intuitive and safe touchscreen interfaces in vehicles continues to grow, the integration of ultrasonic haptic technology, such as that developed by hap2U/Vibra Nova, holds great promise. By leveraging the expertise of companies like Polytec in characterizing and optimizing these systems, the automotive industry can deliver enhanced user experiences while prioritizing safety and minimizing cognitive strain associated with touchscreen interactions.
