The Cloud Walker: a lightweight, user-driven exoskeleton for people with Spinal Cord Injuries

“We wanted to make a new type of walking brace for people with spinal cord injuries,” explains Gerwin Smit of the Delft University of Technology (TU Delft). As part of the Convergence programme, Smit teamed up with Rutger Osterthun of the Erasmus Medical Center (Erasmus MC) in Rotterdam to produce ‘The Cloud Walker’ – a light-weight exoskeleton which enables the user to generate their own walking movement without the need for motors.

Smit is a specialist in prosthetics and orthotics at TU Delft’s Department of BioMechanical Engineering, whilst Osterthun is a researcher and specialist in rehabilitation medicine in the field of spinal cord injury (SCI) at the Erasmus MC and Rijndam Rehabilitation Center: “Improving mobility is one of the key issues for people with SCI and this is a very nice way to create opportunities for one group of these people – specifically those with paralysis in the lower body but who still have the use of their arms.”

Different types of walking aids are already available for people in this group says Smit: “At one end of the spectrum is a new type of exoskeleton which uses a lot of motors. These are nice devices but they’re also expensive and difficult to work with because they’re heavy – around 25 kilos. Then at other end of the scale, you have the mechanical orthosis, which are like leg braces, and these are typically quite rigid. So we wanted to create an orthosis with an elastic coupling between the legs that gives the user more freedom to generate their own walking motion so they don’t need motors.”

Using an existing mechanical orthosis as a basis, they decided to insert springs to create elastic couplings to make the whole brace less rigid – an idea suggested by another member of the team, Master’s student Thomas van Hengel, of TU Delft: “I saw one small mention of this idea of using springs in the literature from about twenty years ago. So we thought it would be worth trying to build on this idea, especially as there have been so many developments in mechanics and materials since then.”

The secret to this new orthosis is the energy storage in the springs says van Hengel: “The older versions had this stiff coupling between the right and the left leg so if the right leg was going forward, flexing, the other leg was extending. But the idea of the Cloud Walker is that when you lift your foot, because the springs are already under tension, the leg goes forward when the weight is lifted off the leg.”
“Using springs, we have so-called Force couplings,” adds Smit, “which gives the user the freedom to choose their motion and move more naturally.”

At around five to seven kilos, the prototype Cloud Walker is certainly lighter than many other types of walking assistance for paraplegics and the upcoming test phase should prove just how easy it is to use. “And compared to previous types of rigid orthosis, which take a lot of energy to move, this one should decrease the energy cost of each movement,” points out Osterthun.

Convergence collaboration
So what has working on a Convergence project brought the researchers? Smit: “We aimed for a smart and affordable solution for a large group of people that can be tailored to the needs of the individual patient. In order to do that, we needed to know both the technical aspects and also the needs of the patients. So Convergence brought these things together.”
And Osterthun: “Actually, it’s been very inspiring because the TU guys think differently from us. Sometimes it’s quite difficult because we have to try and speak each other’s language but the big advantage is that you get much more from working with people in different fields. Really a case of one plus one equals three!

Gerwin Smit
TU Delft

Rutger Ostherthun
Erasmus MC & Rijndam Revalidatie