A climbing robot needs to use its adhesive patches over and over again as it scales a slope. Replacing the adhesive at each step is generally impractical. If the adhesive or attachment mechanism cannot be used repeatedly, then the robot must carry an extra load of this adhesive to apply a fresh layer with each move. Common failure modes include tearing, contamination by dirt, plastic deformation of fibers, and damage from loading/unloading. A gecko-like fibrillar adhesive has been developed that has been shown useful for climbing robots, and may later prove useful for grasping, anchoring, and medical applications.
The material consists of a hierarchical fibrillar structure that currently contains two levels, but may be extended to three or four levels in continuing work. The contacting level has tens of thousands of microscopic fibers made from a rubberlike material that bend over and create intimate contact with a surface to achieve maximum van der Waals forces. By maximizing the real area of contact that these fibers make and minimizing the bending energy necessary to achieve that contact, the net amount of adhesion has been improved dramatically.
The suspension structure consists of millimeter-scale fibers that are bonded to the contacting level through a wet assembly step. These millimeter-sized fibers serve as a discretized way of both conforming to roughness on the surface and distributing the overall climbing loads down to the individual contacts. These structures have been tested on an experimental testbed meant to determine the contact forces very exactly, and have also been demonstrated by hanging weights off of a patch adhering to a variety of walls (glass, metal, wood, plastic, drywall, etc).
This material is fabricated via a molding process. A new process has been developed at JPL to make this process simpler, more reliable, and to allow new geometries not previously possible. These new geometries will make the adhesive and the reliability significantly better, and will drive down cost and development time.
The process involves using optical lithography to make a master pattern, and from this master pattern, making a reusable master mold that is used to cast the adhesive strips. To create the master photoresist pattern that will be used to make the master mold, a self-aligned double exposure technique was used. Two different angled UV exposures are performed using a single opaque pattern on a transparent wafer. This simplifies fabrication considerably.
A second advantage of this technique is the ability to achieve right-angle wedgeshaped structures with both sides of the wedge leaning to the same side, i.e., an actual overhang of the fibers, which is more like the arrangement of a gecko foot’s fibers. A third critical difference is the use of a standard positive Novalac photoresist, which has a wide process latitude.
The new microfabrication process has allowed the shape of the wedge-like fibers to be controlled. Prior to these process improvements, only right-angle wedges had been fabricated. Now, the process not only allows for increased control over the angle of these fibers, but is also much more reliable, manufacturable, and cost-effective.
This work was done by Aaron Parness and Victor E. White of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48156
This Brief includes a Technical Support Package (TSP).
Fibrillar Adhesive for Climbing Robots
(reference NPO-48156) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) focused on "Fibrillar Adhesive for Climbing Robots," identified by the reference NPO-48156. It outlines advancements in adhesive technologies that have significant implications for climbing robots and other applications in aerospace and robotics.
The primary innovation discussed is a fibrillar adhesive that utilizes hierarchical structures to enhance adhesion on various surfaces, including glass and wood. This technology is particularly relevant for climbing robots, which require effective adhesion to navigate vertical and complex surfaces. The document references previous demonstrations conducted by Dr. Aaron Parness at Stanford University, indicating that the JPL technique aims to improve upon these results by reducing the elastic springback of wedge fibers, thereby enhancing the adhesive's performance.
The document also includes technical details about the forces at play in the adhesive's operation, such as bending forces and van der Waals (vdW) forces, which are critical for understanding how the adhesive functions at a microscopic level. The hierarchical design of the adhesive is emphasized, suggesting that its multi-layered structure contributes to its effectiveness.
Additionally, the document provides information on the fabrication processes used to create these adhesives, including a "Self-Aligned Double Exposure" process and a wet assembly process for achieving the desired hierarchical structures. These processes are essential for producing the adhesives in a way that maximizes their performance in real-world applications.
The Technical Support Package serves not only as a technical document but also as a resource for potential commercial applications of the technology. It is part of NASA's Commercial Technology Program, which aims to disseminate aerospace-related developments that have broader technological, scientific, or commercial relevance.
For further inquiries or assistance, the document provides contact information for the Innovative Technology Assets Management team at JPL, encouraging collaboration and exploration of these advancements.
In summary, this document encapsulates the innovative work being done at JPL on fibrillar adhesives, highlighting their potential to revolutionize climbing robotics and other fields through advanced material science and engineering techniques.
