Understanding people to design better prosthetic hands and arms
We learn to use our hands as babies. We spend a lot of time just looking at our hands, and playing with things. By the time we’re old enough to think about everything we use our hands for, we don’t. We just take them for granted.
But what if you lost a hand? Would you want to spend years learning how to use a prosthetic replacement?
Our Head of School of Energy and Electronic Engineering, Professor Peter Kyberd, knows that isn’t the case. He’s spent years making prosthetic hands and arms. Crucially, he’s spent years talking to the people who need them, to understand what they want.
Peter explains, ‘Most people don’t want to spend months and months learning how to use a prosthesis. So the aim is to design something which is easier and faster to use. More subconscious, more natural.’
Peter studies the design of the mechanism, looking for ways to make it more robust or useful. He also looks closely at the way humans use their hands. This helps us understand how to make the prosthetics easier to control, in order to create something which is actually practical, that somebody both wants to and will use.
Not every design of prosthesis is practical. The challenge is designing limbs that will be used in the real world. The limbs have to be reliable, light enough to be carried and easy enough to be used. That, to Peter, is what makes the job so difficult and so interesting.
There are some advanced hands on the market with powered wrists and multiple driven fingers with many joints. It’s all possible. But the majority of users elect to use something very, very simple.
‘They don’t want to make their life more complex with something which is an elegant piece of engineering but is actually hard to use.’
Powering and controlling the device is a key challenge. There are two options. An unmotorised prosthesis uses a harness to capture the relative movement of different parts of the body. This can be used to open and close the hand, or move the elbow.
But sometimes the nature of an injury makes the level of effort required too high. So electric motors need to be added. Then the challenge is instructing it in a way that is easy and effective. Electrodes on the forearm can detect muscles contracting. This generates an electrical signal can then be amplified and used as an input. This works well with simple movements. But once you want to control more than one motion (a hand and an elbow), it becomes much trickier to do it simply and quickly.
A greater input
A hand with multiple fingers or a powered wrist needs more inputs. You can control it one joint at a time, switching between joints. Or you can use a different body movement – say, raising an elbow at the shoulder instead of switching from the prosthetic hand to wrist to rotate it – most people would prefer to do the quicker and uglier action.
It is tempting to choose the quicker option, but it can cause injuries through overuse, so may have long term consequences for the user.
Today, it is possible to switch movements with a smartphone. Great if you want to adopt a particular grip for a period of time. Not so great if all you want to quickly change the grip to shake someone’s hand. For everyday life, you need a grip that is more general.
There are lots of interesting designs of artificial hands but they’re not being used by people, and that’s because they are hard to use. Peter’s goal is to make more complicated hands that are easier to use. By finding technical solutions so that people want to use them and are able to do so without effort. It’s all about getting the complexity inside, but making the execution simple for the user. As Peter says:
‘Prosthetics is about people. The engineering is interesting but I wouldn’t want to get involved in a project that didn’t have at least a hope of making a difference to people.’