Modeling and experiments of soft-finger contacts and friction limit surface in robotic grasping

A new theory in contact mechanics for modeling of soft fingers is proposed to define the relationship between normal force and radius of contact for soft fingers by considering general soft materials, including linear and nonlinearly elastic materials. The results show that the radius of contact is proportional to the normal force raised to the power of γ which ranges from 0 to ⅓; that is, the power-law equation a = cN γ where a is the radius of contact, N is the normal force, and c is a proportional constant. Experiments were conducted to validate the theory using artificial soft fingers made of various materials such as rubber and silicone. Results for human fingers are also compared.; We also investigate the influence of size and material properties of fingertips on the power-law equation for soft-finger contacts. Fingertips made of different materials of various sizes are tested, and the parametric relationship between normal forces and radii of contact is found. The experimental results validate the power-law equation for soft fingers with large deformation.; Finite element analysis is employed to further investigate the soft-finger contact mechanics. Three fingertips of the same material but with different sizes are analyzed. The numerical results are compared with experiments as well as the power-law theory.; The generalized model for contact pressure distribution is derived, and experiments are conducted using various fingertip configurations. The experimental results show that the Hertzian model of circular pressure distribution cannot be used in soft fingers with nonlinear elastic deformation.; The results of the power-law theory relating the contact radius with the normal force can be combined with contact pressure distribution to formulate the friction limit surface for anthropomorphic soft fingers. The results of the contact mechanics model and pressure distribution for soft fingers can facilitate the construction of numerical friction limit surface. (Abstract shortened by UMI.)...