Evaluation of Internal Curvature on Suction Cup Performance

As a widely used solution in nature for adhesion and manipulation, suction cups have been introduced to the industry and daily usage. However, in terms of the inner surface, biological suckers are usually curved, instead of the commonly straight surface among artificial suction cups. In this paper, passive suction cups with different inner curvatures are tested under various conditions to evaluate the influence of inner curvature on suction performance. Specifically, the internal curvature is described by a hyperbola, and the test conditions include wet/dry surfaces, substrates with different curvatures (cylinders and spheres), and different tilt angles. A following series of experiments is also presented to evaluate how inner curvature affects, by comparing the performance with/without curvature in the upper/lower part. Results show that the inner curvature helps the suction cup form a seal at a shorter pressing distance and reach higher suction force quickly. Too much curvature limits the deforming capability, resulting in sealing difficulties but high suction force. The lower part curvature helps the suction cup conform to the substrate, and the upper part curvature decreases the required preload and works to conform in the case of tiny objects. These findings provide new perspectives for designing custom suction cups for future robots.