Work Description

Title
Release Chamber Enables Suction Cup to Delaminate and Harvest Fluid

Authors
Xiangyun Bu, Yihao Geng, Siyuan Yin, Liyan Luo, Cameron A. Aubin, Talia Y. Moore

Corresponding Author
Talia Y. Moore
taliaym@umich.edu

Description
Suction is a useful strategy to grasp objects or anchor a body, especially when prolonged contact is desired. For passive suction cups, detachment requires manual delamination, which cannot occur autonomously. Active suction cups detach via equalizing pressure in the suction cavity with the surrounding environment, either by adding fluid (e.g., from a compressed air source) or reducing the cavity volume. While this detachment mechanism can be autonomous, it is inefficient, resulting in a net zero or loss of fluid. A more efficient detachment mechanism would enable multiple iterations of attachment and detachment without requiring additional fluid. To address this need, we designed a suction cup with a secondary release chamber embedded in the contact ring. The release chamber triggers delamination by deforming the shape of the contact ring. Through empirical testing, we found the optimal location and geometry of the release chamber. Our design allows for reliable detachment with a 5~mL decrease in release chamber volume, regardless of the adhesive suction force. Because the release chamber is a closed system, attachment and detachment results in net gain of fluid. Therefore, we propose a novel secondary benefit of adhesion via suction: harvesting fluid to power other pressure-driven soft robotic systems.

Software
All CAD files were created using SolidWorks 2022 Student Version.

Contents
This ZIP archive includes CAD models for the different suction cup designs that were used to empirically sweep the parameter space.

The folder "Suction Cup exploded view" shows the exploded view of the suction cup assembly, which shows how the pieces should be put together. Each suction cup is 1 top part glued to 1 bottom part.

The folder "Top Part Mold" is universal across all suction cup configurations.

The folders beginning with "Fig4_*" include the molds of all suction cup bottom part configurations shown in Figure 4 of the paper:

(b) Variation in release chamber locations

(c) Variation in membrane thicknesses

(d) Constant volume with varying release chamber areas

(e) Constant area with varying release chamber heights

(f) Constant height with varying release chamber areas

Design Notes

The unit area of the release chamber is denoted as α = 77.45 mm².

To vary the release chamber area, the central angle of the fan-shaped sector was adjusted. This changes the angular extent of the chamber while maintaining its radial distance from the center.

To vary the release chamber height, inserts were fabricated using molds and glued into the cavity to reduce the chamber's internal height.

Fabrication

All CAD files were created using SolidWorks 2022 Student Version.
We designed 3D printed PLA molds to construct our suction cups in two primary parts. We designed the molds using Solidworks 2022 (Dassault Systemes, Waltham, MA, USA) and manufactured the molds using an FDM (Fused Deposition Modeling) 3D printer (Ender-3 V3 SE, Creality, China).
The upper part of the suction cup is funnel shaped, with a conical center (29 mm diameter) that vertically bounds the suction chamber and connects it to the source of suction, and a flat peripheral area that attaches to the bottom part in height, with an inner diameter of 29 mm and an outer diameter of 64 mm.

The bottom part laterally bounds the suction chamber, encloses the hollow release chamber, and is the portion that will be in contact with the surface. To form the release chamber, we 3D printed the desired shape and added it to the bottom mold before adding the silicone. The shape of the release chamber is a 48.5 degree arc of a circle concentric with the center of the suction cup.

We used Dragon Skin 20 silicone (Smooth-On, Macungie, PA, USA) to fabricate the suction cups. After combining a 1:1 ratio of the A and B Dragon Skin 20 silicone prepolymer in a centrifuge mixer, we poured the mixture into the PLA molds and degassed in a vacuum chamber for 10 minutes. Next, we cured the molded forms in an oven at 70 ◦C for 25 minutes. We then inverted the bottom part (so that the release chamber is facing upwards) and fused it to the top part with more Dragon Skin 20 prepolymer, then cured it in an oven at 70 ◦C for another 25 minutes. We used silpoxy (Smooth-On, Macungie, PA, USA) to connect one silicone tube (1/8 in outer diameter, 1/16 in inner diameter) to the suction chamber (at the top of the cone) and one to the release chamber. These tubes can be added to any source of vacuum or compressed air. Here, we connected these tubes to empty syringes to facilitate precise changes in volume. We preset the first syringe with zero volume before connecting it to the suction chamber and the second syringe with a positive volume prior to connecting it to the release chamber.