John Kang Liquidmetal | BMG Applications
John Kang: Liquidmetal and BMG Precision Robotics Applications
Where people and animals have different kinds of joints to rely on for precise movements, robots can only rely on gears. This is why Douglas Hofmann of the NASA’s Jet Propulsion Laboratory in Pasadena has been researching the applications of bulk metallic glass (BMG’s) in robotic gears. John Kang of Liquidmetal Technologies presents some of the findings of Hoffman and his colleagues, along with his thoughts as the chairman of the leading commercial manufacturer of amorphous alloys.
Amorphous alloys (the generic name of Liquidmetal) get their name from the fact that their atomic structure is closer to that of liquid rather than conventional metals. When the alloys are melted into a liquid and cooled rapidly enough out 1,832 degrees Fahrenheit (1,000 degrees Celsius) per second – they can be trapped in their “liquid” state, giving them an amorphous structure rather than the crystalline structure of other metals. When this glassy material is produced in parts greater than about 1 millimeter it’s called bulk metallic glass a.k.a. “BMG”.
Among other desirable qualities like strength and durability, the process of producing BMG is highly precise. Because the alloy has a low melting point, scientists use injection molding techniques usually seen in the manufacturing of plastic components, and BMG can be produced with unprecedented precision for metal molding. Tolerances can be made to fall between 0.05 and 0.1 microns.
This is important for robotics because high-precision movements in robots rely on strain wave gears, which is a type of gear which includes a metal gear that flexes as the gear spins. Every time an advanced robot catches a ball, or picks up a pen, notes John Kang of Liquidmetal Technologies, a series of strain wave gears are most likely behind the movement.
Strain wave gears are very difficult and expensive to mass produce because of their high tolerance and durability requirements. When produced using steel or steel-based alloys, the parts of the gear need to be tooled precisely, at the sub-micron level. In fact, strain wave gears tend to be the most expensive part of a robot.
The use of Liquidmetal, John Kang says, or BMG’s can drastically cut down the cost of manufacturing by reducing rejected parts and increasing durability. In addition to the cost-saving benefit, BMG’s can also be run dry (or without lubricant), and operate at extremely low temperatures (-328 degrees Fahrenheit or -200 degrees Celsius), making them ideal for space applications.
Using current gearing technology, NASA’s Mars Curiosity rover expends energy heating up grease lubricant every time it needs to move, notes John Kang. To John Kang, Liquidmetal gears used in an extraterrestrial rover may be able to reduce or eliminate this expenditure.
In his paper published by Advanced Engineering Materials, Hofmann says, “Mass producing strain wave gears using BMGs may have a major impact on the consumer robotics market. This is especially true for humanoid robots, where gears in the joints can be very expensive but are required to prevent shaking arms. The performance at low temperatures for JPL spacecraft and rovers seems to be a happy added benefit.”