Development of a Wearable Exoskeleton for People With Duchenne Muscular Dystrophy

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"The portability of CompactRIO helps with the integration with the wheelchair and expands the mobility. Since LabVIEW software integrates easily with different third-party MAXON drivers, this resulted in an even more flexible platform."

- Joan Lobo-Prat, University of Twente

The Challenge:
Developing an arm support that gives people with Duchenne muscular dystrophy a more independent and social life.

The Solution:
Using CompactRIO and LabVIEW to develop the A(bility)-Gear that can adapt during the lives of patients for their different needs.

Author(s):
Joan Lobo-Prat - University of Twente
Peter N. Kooren - VU University Medical Center

Duchenne Muscular Dystrophy
Duchenne muscular dystrophy is caused by a mutation in a specific gene in the X-chromosome, which is why Duchenne is only found in males. Duchenne causes loss of muscle control during childhood. It has a significant impact in the world since 1 out of 3,600 males has this disease. The life expectancy has recently improved to an average age of 35 due to new medications.

About Flextension
The Flextension Foundation was founded in 2007 in response to the demand from the Duchenne community to find technological solutions for boys and young men with Duchenne muscular dystrophy to improve their quality of life. The board of the foundation consists of volunteers working in different universities and volunteers who are active in the Duchenne community. The Flextension Foundation aims to develop new tools that improve the quality of life for boys and young men with Duchenne.

Due to longer life expectancy, the needs for these young men change. The wheelchair is a good current solution for mobility, which is why we focused on the movement of the arms with this project. Improved arm movement can help with eating, taking care of personal hygiene, using computers, writing, reading, and interacting socially.

Current market solutions for arm movement are mostly passive or for rehabilitation, not for everyday use. The rehabilitation devices are often big and not mobile. Boys need these devices around the age of 12, when the muscular strength decreases significantly. Also around this age boys become more conscious about their appearance, and the need to fit in with their peers becomes important. This is why a biomechanical support solution needs to be subtle and visually hidden, or something that looks “cool” and can be worn with pride.

The current market solutions do not give enough support for the later stage of the disease. They only support the weight of the arm and do not consider the influence of joint stiffness. This provides vertical assistance, but there is also a significant need for horizontal assistance.

A(bility)-Gear
The first project of the Flextension foundation, the A-Gear project, was initiated in 2012. The project aims at developing a natural arm support that adapts to the changing needs of people with Duchenne. The Flextension A-Gear project was founded by STW, patients' organizations, and companies. The project is carried out by PhD students in four universities: VU University Medical Center, TU Delft, Radboud University Medical Center and the University of Twente.

We developed the A-Gear to address this need. There are two models of A-Gear, a passive and an active version. The passive version provides weight compensation of the arms. It does not use any motors, but uses springs to accomplish this. Because of the changing needs, there is also the active model. This uses motors to deliver extra support. The active model can build on the passive model, providing users with one product that can adapt to changing needs.

The passive model removes the influence of gravity, which removes the weight of the arm. This means we can use smaller motors for the active model. The arms can become stiff due to the lack of movement, and the motors aid in going through this stiffness and helps the joints. This support makes it possible to do day-to-day activities. The A-Gear features four degrees of freedom, one in the elbow and three in the shoulder. The body helps users be able to wear the A-gear. In Figure 1, you can see how the A-Gear would be worn. The upper legs serve as an anchor, and from there it moves up to the shoulder. Another movement point at the hips enables the bending movement. This is passive, but significantly extends the movements that can be made.

FlexTension from Flextension on Vimeo.

We chose NI because of the modular nature of the CompactRIO platform, which features different C Series modules. Some control the motors in the active version of the A-Gear, others allow the sensors to connect to the CompactRIO so the motors know what to do. The CompactRIO also contains an FPGA, which can communicate with the motors through high-speed CAN protocol using the NI 9853. We used the CompactRIO real-time processor to do the processing within the time limit of 10mS, receiving the sensor information through the NI 9205 and processing this to know which commands to send to the motors. This timing requirement is needed because if the motors take longer to respond, the movement will not feel natural. We made the investment for the current system setup, but we can use the same setup in the future because of the system’s modularity. We can even easily alter the system by changing the C Series modules. Also, portability of CompactRIO helps with the integration with the wheelchair and expands the mobility. Since LabVIEW software integrates easily with different third-party MAXON drivers, this resulted in an even more flexible platform.

Several NI personnel helped with development, from sales to support, and determined the best solutions for hardware and software. We also attended different courses to improve the development of the project.

Summary
We designed and developed the A(bility)-Gear to respond to the needs of the young men and boys dealing in their everyday lives with Duchenne muscular dystrophy. The A-Gear can adapt to changing needs of people with Duchenne to improve their quality of life.

www.flextension.nl

Author Information:
Joan Lobo-Prat
University of Twente
Drienerlolaan 5, 7500 AE
Enschede
Netherlands
j.loboprat@utwente.nl

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