Why Settle For Two Arms When You Can Have Four?

Researchers at MIT's d'Arbeloff Laboratory have unveiled a pair of wearable robotic limbs that would make Dr. Octopus proud.

Supernumerary Robotic Limbs (SRLs) are wearable robotic limbs that, instead of replacing missing limbs, endow the user with an extra set. And unlike conventional exoskeletons, these limbs augment the workspace and skills of the user.

The MIT researchers presented their latest SRL prototypes yesterday, June 2nd, at the IEEE International Conference on Robotics and Automation (ICRA) in Hong Kong. One model features a pair of limbs that springs from the shoulders, and another with limbs that extend from the waist.

After strapping on the device, you could work on tasks that are above your head, or when your natural arms are busy with other things. In the example below, a worker can be seen propping up an object to the ceiling with the SRLs while his natural hands are free to hammer or screw it into place.

Another application is to open doors or ring doorbells while your hands are busy holding on to something.

Why Settle For Two Arms When You Can Have Four?

Why Settle For Two Arms When You Can Have Four?

Evan Ackerman from IEET Spectrum explains how it works:

The SRL shoulder robot uses two arms mounted on your shoulders such that the reaction forces on them are aligned with the spine. Each arm has five degrees of freedom, with interchangeable and customizable end effectors, and the complete systems weighs about 4.5 kilograms (10 pounds).

What's tricky about having a pair of shoulder arms is getting them to do what they're supposed to do without having to control them with your other arms, which would kind of defeat the purpose of the entire setup. Instead, the SRL watches what you're doing with your arms to decide how to move. It does that by monitoring two inertial measurement units (IMUs) that the user wears on the wrists. A third IMU sits at the base of the robot's shoulder mount, to track the overall orientation and motion of the SRL.

The SRL uses the gyro and accelerometer data from the IMUs to make a prediction (based on a model that's been created by demonstration learning) about what would be the most helpful, proactive position for its own arms. If you put your arms up above your head, for example, the SRLs raise above your head too, because it figures you're trying to hold something up. Using their SRL prototype, the researchers are testing different "behavioral modes" to program the limbs to do what they want.

Why Settle For Two Arms When You Can Have Four?

Much of this work is being funded by Boeing, which is trying to find ways to keep its aging workforce of aircraft builders active, and to prevent injuries.

Why Settle For Two Arms When You Can Have Four?

The researchers say that their design works better in certain contexts than an exoskeleton, which places all of its force wherever arms and legs are positioned.

Read the entire article at IEET Spectrum.

All images: d'Arbeloff Laboratory.