Contact Mechanics for Soft Hemi elliptical Robotic Fingertip

To increase the robustness and stability of grasps during manipulation, soft fingertips are preferred to use in the gripper of robotic and prosthetic hand. Establishing a relationship between imposed load and contact area is an important step to understand the governing mechanics behind it. A new analytical model for hemi-elliptical soft fingertip is established herein. This is performed by the use of nonlinear contact-mechanics to have a relationship that relates the normal force with the radii of contact as a power-law equation. Experiments were conducted in order to verify this model. The soft fingertips used herein are made from three types of silicone rubber. The results indicated that the radii of contact ellipse are proportional to the imposed load raised to the power of γ that falls within (0 ≥ γ ≥ 1/3) and ellipticity parameter K. The magnitude of K is proportional to the ratio of curvature radii of hemi-elliptical shape raised to the power of α that falls within (1 ≥ α ≥ 0.636). The power indices α and γ are dependent on the material hardness as well as the geometry of fingertip. This new model incorporates Hamrock model for the linear elastic materials of elliptical contact with (α = 0.636) and Kao model for the non-linear elastic materials of circular contact with (K =1). Weighted residuals least-squares curve fitting was used for the purpose of fitting the experimental results. The experimental results supported the proposed theoretical prediction. In conclusion, the hemi-elliptical shape fingertips are better in contact properties as compared to the hemi-spherical shape fingertips.