Study and development of an ergonomic haptic interface using flexible coils

The world of haptic is an emerging field of research with rapidly evolving technologies. Researchers are still looking for the optimal solution to create a haptic device that can provide a realistic touch sensation. Vibrations, forces, and temperatures are the stimuli involved in the majority of the touch experience. For what concerns the rendering of texture, i.e., generating vibratory cues, the most widespread technology is high-performance piezo actuators, but even if this technology has multiple limitations. The most critical ones are their limited capability of generating low-frequency responses and their lack of flexible models. These characteristics are crucial for the creation of a realistic haptic interface that could also be easily integrated into wearable devices. This thesis aims at investigating the use of flexible PCB coils in haptic applications. Flexible PCB coils are a new technology which can be used to create voice actuator-style haptic interfaces that can withstand bending stresses and produce low-frequency vibrations. Voice-coil actuators are systems based on the electromagnetic force interaction between a coil and a magnet. This force can be harnessed with the use of a membrane to transfer vibrations to human skin. The first part of the thesis focuses on the physics of such a device with the creation of a mathematical model of the entire force transmission chain, considering also how finger-pulp skin reacts to the device stimuli at different frequencies and amplitudes. Next, the electronics required to drive the proposed device is presented. Finally, the last part reports the design and testing of a series of prototypes that will help us understand the limitations and potential of this technology.