A nonlinear rheological model for the ultrasonically induced squeeze film effect in variable friction haptic displays

A squeeze film induced by ultrasonic vibration between two solid surfaces in contact can dramatically reduce the friction between them. This phenomenon, so-called the squeeze film effect, has been utilized in variable friction tactile displays for texture rendering purposes. Such tactile displays can provoke a haptic sensation to a finger pad in a controllable way. A real-time adjustment of the coefficient of lateral friction between the human finger pad and the tactile display can be accomplished by modulating the vibration amplitude of the tactile panel. Therefore, driving a reliable friction model is a key step towards designing and controlling tactile displays utilizing the squeeze film effect. This paper derives a modified Herschel- Bulkley rheological model to express the lateral friction exerted on a human fingertip via an air squeeze film as a function of the operating parameters such as the driving voltage amplitude, the finger sliding speed, and the contact pressure. In contrast to the conventional Coulomb friction model, such a rheology model can account for the sliding velocity dependence. This modeling work may contribute to the optimal control of the ultrasonic variable friction tactile displays.