The chemical element gallium could be used as a new reversible adhesive that allows its adhesive effect to be switched on and off with ease
Some adhesives may soon have a metallic sheen and be particularly easy to unstick. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart are suggesting gallium as just such a reversible adhesive. By inducing slight changes in temperature, they can control whether a layer of gallium sticks or not. This is based on the fact that gallium transitions from a solid state to a liquid state at around 30 degrees Celsius. A reversible adhesive of this kind could have applications everywhere that temporary adhesion is required, such as industrial pick-and-place processes, transfer printing, temporary wafer bonding, or for moving sensitive biological samples such as tissues and organs. Switchable adhesion could also be suitable for use on the feet of climbing robots.
The principle is actually quite simple: Above 30 degrees Celsius, gallium metal is liquid, and below 30 degrees it is solid. So if a drop of liquid gallium is introduced between two objects and then cooled to less than 30 degrees, the gallium layer solidifies and sticks the two objects together. When it is time to separate the objects, the temperature is raised to transition the gallium layer to its liquid state and they can be pulled apart with a small amount of unloading force. As an adhesive, gallium works in a similar fashion to hot glue, widely used in DIY applications. The difference is that far less heating and cooling are sufficient in the case of gallium, it lifts much more easily and cleanly from the surface, it is highly repeatable, and it is electrically conductive.
A soft actuator using electrically controllable membranes could pave the way for machines that are no danger to humans
In interacting with humans, robots must first and foremost be safe. If a household robot, for example, encounters a human, it should not continue its movements regardless, but rather give way in case of doubt. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart are now presenting a motion system – a so-called elastic actuator – that is compliant and can be integrated in robots thanks to its space-saving design.
The actuator works with hyperelastic membranes that surround air-filled chambers. The volume of the chambers can be controlled by means of an electric field at the membrane. To date, elastic actuators that exert a force by stretching air-filled chambers have always required connection to pumps and compressors to work. A soft actuator such as the one developed by the Stuttgart-based team means that such bulky payloads or tethers may now be superfluous.
Many robots have become indispensable, and it is accepted that they may be dangerous to humans in their workspace. In the automotive industry, for example, they assemble cars with speed and reliability, but are well shielded from direct contact with humans. These robots go through their motions precisely and relentlessly, and anyone who gets in the way could be seriously injured.
Robots with soft actuators that cannot harm humans, on the other hand, are tethered by pneumatic hoses and so their radius of motion is restricted. This may be about to change. “We have developed an actuator that makes large changes in form possible without an external supply of compressed air”, says Metin Sitti, Director at the Max Planck Institute for Intelligent Systems.