Design and modeling of a fingertip force sensing system without tactile interference

It's important to measure the force used during fingertip manipulation without affecting the natural sense of touch when digitizing the skills of experienced craftsmen. However, most force sensors need to be placed between the skin and the objects which can interfere with the natural skin sensation. Here, we developed a wearable fingertip force sensing system that can monitor fingertip force without affecting tactile sensation. The system measures the changes of blood volume in the fingertip by photoplethysmography (PPG) to obtain the fingertip force during manipulation. A hemodynamics model of fingertip blood flow was established, and variations in fingertip blood vessel diameter under force conditions were simulated and analyzed. The scalability of the hemodynamics model is verified by experiments with different operating contact angles. This work sheds new light on areas such as digitization of the skills of experienced people and human-machine interaction.