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Abacus: First New Rotary Transmission Design in 50 Years

SRI International robotics engineers have developed the first new rotary transmission design since Harmonic Drive introduced its gear system, based on a mechanism known as a strain wave gear, in the 1960s. Harmonic gears are compact, have high gear ratios, and don't have backlash, but they are also expensive. Harmonic Drive is a partner in the new project - the company has licensed the Abacus design from SRI and is collaborating with them to commercialize it. The new Abacus drive is a pure rolling transmission - there are no parts that rub or slide against each other, only parts rolling against other parts. Rubbing and sliding result in wasted energy, and conventional transmissions are typically only 50 percent efficient. SRI International researchers say the new drive has efficiency in the high 90s. The Abacus drive has beads that roll in and out of a groove with a variable diameter, which causes the beads to effectively change their diameters depending on where in the groove they are.

Topics:
Automation Motion Control Motors & Drives Power Robotics

More From SAE Media Group

    Transcript

    00:00:00 the technical description would be pure rolling cycloid with variable effective diameter rollers [Music] my name is Alexander karma I'm a senior researcher at SSRI international in the robotics group and here we are Robo business and we're showing off a lot of new fun things today one that I'm really excited about is called abacus Drive

    00:00:21 it's the first time we've announced it it's a new rotary transmission do you think it's the first rotary transmission since the harmonic drive came out in 1960s in most applications that involve a motor you want the motor to spin a lot faster than the output this just has to do with motor physics you can't really get around it so typically you have a transmission that exchanges the speed

    00:00:42 for the torque essentially in robotic applications today the most common transmission is the harmonic drive and the main reason for that is the very low backlash so this is what we're calling our abacus drive the principle is that these rollers are actually moving in and out of a groove of variable diameter and we're actually changing the geometry in a new axis that you know before this no

    00:01:03 one has really looked at and that that groove a variable diameter is what gives you the pure rolling motion essentially and the name of the drive abacus drive comes from the shape of the beads right there it turns out though that the shape of the bead is actually a design input you can make it anything you want and so here you see in this transmission we use spheres or you can think of them as just

    00:01:23 roller bearings to create the transmission ratio essentially or so here my finger is the input and the outputs on the other side this is a three to one here essentially the areas that we think it's gonna make a really big impact our applications or efficiency matters which is going to be the case more for robotics especially for any kind of mobile robotic platform

    00:01:42 your transmission is only 50% efficient that means that at least half of your energy is going into heat another area that we think is going to matter for robotics is simply having we call low back driving torque in the system be back driven can the system know what the environment is like with this kind of transmission for instance if you're a rounded human and you bump into a human

    00:02:04 you can actually measure the motor torque increase at the motor and then you can adapt to the environment but the last thing is going to be cost so the transmission here is going to be significantly lower cost than Christie's mania extremely fierce so we actually have a really great partner in this it's actually harmonic drive systems they saw something new in the market they got

    00:02:25 very excited about it so we're actually developing it with them right now we're in the process of doing lifetime testing right now and we expect to have beta version drives within the year essentially and then after that we'll be rolling out our first product [Music]