I was introduced to exoskeletons as a graduate student at the University of California, Berkeley where I was fortunate enough to study with Professor Kazerooni whose work focuses on enhancing human capability through exoskeletons. The lab developed devices like BLEEX, which give able-bodied individuals added strength by wrapping a mechanical structure around the body and adding power.
The initial devices were large and required offboard power or loud engines which limited their use. Then the lab developed HULC, the Human Universal Load Carrier, which was a breakthrough exoskeleton developed to help soldiers carry load through unknown terrain.
It followed the same model of BLEEX and other exos in mimicking and adding to the body’s structure, but it utilized gravity and joint alignment and actuation in a way that enabled the device to be run off of on-board power. HULC’s design transfers the load weight around the human body to the ground and added power to the legs only where needed. Professor Kazerooni saw that this technology could be extended to add power where there was a deficit, not just where excess power was needed. My colleagues and I began work in developing the concept of a medical exoskeleton and were met with many challenges- some expected, some not. I was excited by this challenge and the potential to help those who had suffered from a stroke or spinal cord injury, and while I knew the challenge would not be an easy one, it took some time to understand the difficulty of transitioning from developing a device for able-bodied load-carriage applications to one that provides mechanisms for gait rehabilitation.
An exoskeleton for load carriage does not need to provide assistance in all directions. Gravity helps with knee flexion (like when squatting down), so power can be limited to extension. In a rehabilitation device, the patient lacks power or control in both flexion and extension so both must be powered.
In a device built for rugged terrain, the soldier must have full flexibility. Therefore, joints that are not controlled must be free, such as hip abduction to allow for side-stepping. In therapy, we must control all joints even at the cost of reduced freedom by locking them out completely.
HULC was built for use by the army, to be used outside and with trained soldiers. Service could be completed by the users, so regular maintenance was not an issue therefore allowing us to utilize hydraulics to optimize the location of components. In the medical setting, however, regular maintenance and potential leaks were not acceptable while the distribution of weight was less critical, so a more traditional motor system was chosen.
A soldier must be able to quickly take off the exoskeleton for full maneuverability in case of emergency or attack, thus the robot has minimal connection points. In a clinical setting, the patient must be tightly coupled to the device for safety and while donning and doffing must be fast, it does not require the speed a military device does. However, the user must be able to transfer into it with limited to no motion in the legs.
There are many additional challenges that face rehabilitation exoskeletons. While some are similar to those faced in the military or industrial applications, many are unique to the users and settings found in rehab. When I entered that lab more than a decade ago, I did not realize how much this problem would draw me in and become my passion. The challenge of building a robot for gait rehab is one that challenges the engineering mind while never letting us forget who we create for.