SRI Abacus Rotary Transmission SRI has introduced the Abacus transmission, the first new rotary transmission design since Harmonic Drive introduced its revolutionary gear system in the 1960s.

Harmonic Dive gears are amazing, but expensive due to of the kind of precision machining they require. Alexander Kernbaum, a senior research engineer at SRI International wanted to create a product which was less costly, so he came up with an entirely new rotary transmission called the Abacus drive.

The Abacus drive, named because its components look like the beads of an abacus, is a pure rolling transmission. No parts of the Abacus transmission rub or slide against each other (like gear teeth). Instead, the beads in the drive roll in and out of a groove with a diameter that varies. This causes the beads to effectively change their diameters depending on where in the groove they are, resulting in a cycloidal motion similar to what you see in Harmonic Drive gears.

Rubbing and sliding affects the efficiency of transmissions, with the average conventional transmission only functioning at approximately 50%. Kernbaum says that Abacus has an efficiency “in the high 90s,” a massive improvement. Furthermore, the Abacus drive has a low backlash, very low backdriving torque, and is a lower cost than a harmonic or similar strain wave gear system, because it’s easier to manufacture.

In fact, the drive is such a beneficial concept, that Harmonic Drive, the principle manufacturer of Harmonic Drive gears has become a partner in the project. It has licensed the Abacus design from SRI and is collaborating with them to commercialize it.

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Source: IEEE Spectrum