how a amputee controls a bionic arm.
In: Technology
There are actually a bunch of different ways to control a prosthesis! The prosthetist (doctor or engineer who specializes in replacement limbs) selects from a bunch of different systems depending on what the patient needs.
The arm could contain a sensor that detects the motion of the arm and translates it into actions. For example, turning your wrist clockwise could close your fingers, and turning it counterclockwise could open them. This is a very common way to control bionics, since it’s reliable, cheap, and works well with many different medical conditions and body shapes.
Some arms use EMG sensors (electromyographics). The chemical reactions that power your muscles have an electrical signal, which can be detected and amplified. These are often given to patients with wrist amputations – the muscles that bend their fingers still work, but aren’t connected to anything. The prosthesis detects these muscles flexing and converts it to finger motion.
These arms are more complex – the sensors need to be placed just right, and the computer needs to be recalibrated often to detect the right muscle motion.
Some arms directly connect to the nerves that control muscles or the brain itself. These are the most complex prosthetics – the truth is that our current technology, science, and medical knowledge isn’t good enough to make these work very well. We know how the brain communicates with muscles, but not well enough to directly connect a computer to them.
We’ve built some nerve-interfaced prostheses, but they’re not really better than the alternatives yet. That said, there are a ton of discoveries to make and problems to solve.
The most sophisticated modern prostheses combine EMG, neuroscience, and neurosurgery. The doctor gives the patient drugs and treatments to cause the nerves in the arm to grow longer. They then surgically “rewire” the nerves into the patient’s chest, so they flex different parts of the pectoral muscle instead of fingers and the wrist. The prosthetic’s EMG sensors detect these flexes and control the arm. This way, even if a patient’s arm is totally missing, they can still control individual fingers.
When you want to move your arm, your brains sends an electrical signal to the appropriate muscle. So in a bionic arm these signals are picked up and move based on what nerve the signal was sent to. Eg if the forearms nerve moves the forearms, the bionic arm connect to this nerve moves when it detects something.
There’s electronics that picks up the signals sent to the remainder of the arm and translates this to movement.
When you tell a muscle to contract you send a very weak electric signal. The bionic arm will have EMG sensors that pick up the potential difference between a reference point and the signal source (usually the head of a muscle). Data from multiple sources is used to detect the desired movement.
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