FDSense: Estimating Young's modulus and stiffness of end effectors to facilitate kinetic interaction on touch surfaces

We make touch input by physically colliding an end effector (e.g., a body part or a stylus) with a touch surface. Prior studies have examined the use of kinematic variables of collision between objects, such as position, velocity, force, and impact. However, the nature of the collision can be understood more thoroughly by considering the known physical relationships that exist between directly measurable variables (i.e., kinetics). Based on this collision kinetics, this study proposes a novel touch technique called FDSense. By simultaneously observing the force and contact area measured from the touchpad, FDSense allows estimation of the Young's modulus and stiffness of the object being contacted. Our technical evaluation showed that FDSense could effectively estimate the Young's modulus of end effectors made of various materials, and the stiffness of each part of the human hand. Two applications using FDSense were demonstrated, for digital painting and digital instruments, where the result of the expression varies significantly depending on the elasticity of the end effector. In a following informal study, participants assessed the technique positively.