Adhesion-adjustable passive suction cup using an elasticity of hemispherical cap

The passive suction cup can produce adhesion without relying on a pneumatic device, which fundamentally solves the low energy efficiency, large volume, and weight problems of an active suction cup. It is especially attracting the attention of wall-climbing robots, where lightweight is essential. In addition, the wall-climbing robots need a moderately small adhesion when moving on the wall and, conversely, a high adhesive force to be fixed and work for a long time at a specific location. Thus, the adjustability of the adhesive force of the suction cup will expand the versatility of the robot. Here, we develop passive suction cups applying a mechanism that can produce high adhesive performance and can easily control the formed inner pressure. The suction cup consists of an elastic hemispherical cap and a flat brim that contacts with a wall. The cap largely deforms when subjected to indentation and creates a negative pressure returning to the hemispherical shape upon the disappearance of the indentation. The formed inner pressure can be changed by varying the indentation depth. We measure the generated pressure difference depending on indentation depth according to several conditions of the indenter. Furthermore, we also measure vertically and horizontally the pull-off force of the suction cup with various pulling speeds and the peel-off time with various additional loading.