Researchers at Northern Arizona University have developed a robotic ankle exoskeleton that doesn’t just help you get up the stairs if you’re suffering from an injury but could also be fundamental to rehabilitation. Tricia Smith talks to Zach Lerner to hear how...
Zach - It's really easy to make a wearable robot that makes walking more difficult. It's much harder to make a wearable robot that makes walking easier. What I mean by that is, when you add something to the body, when you add heavy motors and batteries, it can actually be detrimental. Especially if you place them on the feet or the lower legs. It's really metabolically expensive. It takes a lot of energy to move heavy limbs.
Tricia - So with the wearable exoskeleton that you've developed, can you explain to me what it looks like and how it works?
Zach - We've designed our ankle exoskeleton in such a way where the heaviest components are located close to the waist, like a location where you would carry a Fanny pack. Then we have cables that travel down the leg and they actuate pulleys on an ankle assembly. Then there's a foot plate and a calf cuff and this rotary joint that's actuated by these cables, and it's driving the foot in a particular direction.
Tricia - What's the difference between using the exoskeletons for rehabilitation and also using it for assistance.
Zach - The device can be controlled to provide torque or forces that interact with the body that work in conjunction with the muscles. The reality is that no one wants to wear a leg brace for the rest of their lives, so we've been developing a technique where we actually provide resistance to the body at a particular point in the gate cycle. It's training muscles to turn on at a particular time when it's most beneficial for efficient walking.
Tricia - By using these exoskeletons in resistive mode, without wearing it, their day is improved.
Zach - That's exactly right. It's been really remarkable how quickly our participants in our clinical resource studies have improved. In as little as 10 sessions over 4 weeks, we've seen a remarkable improvement in their walking speed and in their walking pattern. We can actually make people better. We can improve their underlying function, even when they're not using the device. It's really exciting to think about devices that can go home with individuals and can be used daily for functional training, and to allow a connection between a physical therapist who could remotely monitor their patient's progress by just using the onboard sensors that are embedded into these devices.
Tricia - And when these devices are working in 'assistive mode', how do you make that device able to adapt to a changing environment?
Zach - The approach that we've taken is to embed 4 sensors under the forefoot. This allows us to approximate what the calf muscles are trying to achieve. Using this as a proxy measure for someone's intention, these sensors can capture when someone is naturally speeding up or slowing down or walking on stairs or a ramp. And it's also important that we have control strategies that are able to adapt to different gate patterns. They're able to adapt to different neurological conditions, different people using the device. In some ways, the mechanical design of a wearable robot is the easy part. The control of the device can sometimes be much more difficult.
Tricia - What do you see exoskeleton technology looking like in the future with advances?
Zach - We're going through a really remarkable period of electrification of personal mobility. Electric skateboards, electric scooters, and in the wearable robotics space, we're electrifying joints. We're benefiting from the proliferation of affordable batteries and improvements in battery capacity, the large scale productions of appropriately sized motors. As the wearable robotic space grows in conjunction with electrified mobility, we'll see the benefits of devices that are more affordable and more effective because they're smaller, they're lighter and they can use be used for a longer period.
Chris - Zach Learner there speaking with Tricia Smith.