A small robot with the ability to hoist large loads could have countless applications, not only as a small, inexpensive, disposable, mobile sensor in the realms of search and rescue, surveillance, and environmental monitoring, but also as an actor that could alter its environment. Instead of observing an event, a tiny robot that can produce huge forces could affect the event. It could (possibly in a team) carry a rope ladder to a person trapped in a burning building, or carry equipment and fix the crack it discovers in a dam or bridge.
A directional dry adhesive was developed that enables a 9-g micro-robot with a single actuator to crawl or climb with a payload of 100 times its body weight. Two novel methods of attaining controllable, anisotropic adhesion have been developed; one is based on applying moments to the adhesive pad to decrease contact area and thus adhesion, and the other uses siping of the adhesive material to yield the same result.
To create a small, simple robot with a large hoisting ability, a linear inch-worm gait is chosen. This gait is based on the traditional inchworm motion. The novelty of the gait presented here, however, is that it allows a robot to climb up a smooth, vertical surface using controllable dry adhesives, while supporting large loads, resisting falls due to missed steps, and parking without power consumption.
The gait involves two adhesive pads that are able to move with respect to one another. While one pad supports the load, the other moves up the wall. While this inchworm gait is conceptually very simple, the subtleties of achieving the gait on a vertical surface while providing very large adhesive forces are more complex.
The first challenge is loading the adhesive uniformly to achieve the maximum possible adhesion. This is done through the use of a rigid adhesive pad and a tendon that loads the pad through its center of pressure. The payload is supported by this tendon, which avoids the moment that tends to pitch climbing robots backward.
Most adhesives, including many dry adhesives, require pressure in the normal direction to stick. With only a single degree of freedom, a linkage is required to press one adhesive pad into the surface while removing the other, all while progressing the robot up the wall. To avoid the use of a linkage that adds weight to the robot, a controllable adhesive (capable of being turned on and off with the application of shear force) is used. The adhesive is Poly(dimethylsiloxane) (PDMS) micro-wedges. When loaded in shear (along the surface), the adhesives pull themselves into contact, resulting in large adhesion; when unloaded, the adhesive can be easily removed from the surface. Controllability means that the robot only needs to transfer its weight to the adhesive to make it stick, without having to press it into the surface.
The third challenge is moving the non-engaged adhesive pad up the wall during the “swing” phase of the gait. While controllability allows the easy engagement and release of the adhesive, it does not mean that the adhesive does not stick when sheared in the anti-preferred direction. In fact, a limit curve of the microwedges shows nearly symmetric performance in force space. This is because the wedges simply flip, and the back of the wedge adheres.
For more information, contact Mary Albertson, Senior Licensing Associate, at 650-725-9411.