A software challenge
At a glance, the exoskeleton doesn’t look all that complicated. Mechanical hip joints, knees and ankles, connected by artificial bones. But to control it and achieve the right kind of movement patterns is far from trivial. Motors, sensors and super-fast software algoritms interact to let the user control the movements in a simple and intuitive way.
“The software is definitely a major challenge” says Martijn van der Marel, embedded systems engineer at Project MARCH. “It’s about meticulous control of each component, based on several dynamic parameters. From the user’s joystick, but also from all the sensors involved. Simply, it’s robotics in real time”.
EtherCAT does it
Project MARCH decided on EtherCAT as fieldbus, for reasons of speed and simultaneous capacity. Martijn contacted rt-labs who provided developer licensing. The system contains a main processor and a line-up of local controllers for each sensor and motor. “The developer software by rt- labs allows us to quickly prototype and test new EtherCAT slaves”.
“Our exoskeleton is under continuous development”, says Martijn, “every year, a new team takes over and makes its utmost to improve and refine the design and the functionality. Over 20 students put their studies on hold for a year to spend all efforts on the MARCH project”.
Making it future-proof
The handover between teams means that both hardware and software have to be fully documented, and that the design concept and structures are future-proof. “In that respect, EtherCAT is a valuable asset”, Martijn explains, “since we want high-speed processing of real-time data. And for our next technology leap we aim for a self-balancing exoskeleton, which will require loads of capacity”.
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Put to the test in real life
Each year’s edition of the exoskeleton is built for a specific
person, the pilot, who Martijn points out as the most important member of the team. And the grand finale of the team’s efforts is the Cybathlon, or the Paralympic Bionic Games. It’s a race where the pilot uses the exoskeleton to make her or his way through a number of staged everyday situations such as walking up stairs and navigating uneven terrain.
“It’s a fantastic feeling to get there and to compete against other developers, and to see the real-life benefits of what we’ve done for the year that passed. And – already there and then, new ideas are born for the next edition of MARCH”, concludes Martijn van der Marel.