Robotic Exoskeleton Helps Children with Scoliosis

Children who wear spine braces could gain more wiggle room if a new exoskeleton design proves successful. Each year, 30,000 children use spine braces to treat scoliosis, a sideways curvature of the spine. Most of these users are middle-school and high-school girls who wear the braces under their clothes.

Spine braces work by applying counter-pressure on the spine’s curvature. This prevents the spine from bending further as the child grows and eliminates the for need corrective surgery as adults.

The new exoskeleton spine brace promises to offer users more mobility and comfort, while the device’s control system modulates corrective pressure on the torso in real time. The project is part of a larger scientific effort to develop more lifelike exoskeleton designs.

Conventional braces are typically made of a rigid, two-part plastic shell that fits around the child’s hips and torso and is tightened by a series of belts. By locking the upper body in place, the braces limit movement. Children must typically wear them 12 to 16 hours per day.  

Those braces are stiff, heavy, and uncomfortable. The solution proposed by Sunil K. Agrawal, principal investigator of Columbia University’s Robotics and Rehabilitation Lab (ROAR), was to build an exoskeleton that used robotic technology to adjust to patient movements and permit more flexibility.

Agrawal developed the dynamic robotic spine exoskeleton (RoSE) in collaboration with researchers from Columbia University Medical Center and Bucknell University. Patients who tested it were able to achieve more than 75 percent of their natural torso range while standing, walking, putting on clothes, eating and other daily activities.

The initial RoSE prototype consisted of three rings that encircle the patient’s torso. One was fixed on the hips, while the other two, at abdomen and chest level, moved. These movable rings were manipulated by linear actuators that gave them six degrees of freedom relative to one another as well as to the fixed third ring.

This enabled the rings to adjust their orientation and relative stiffness, providing added support so users could flex their torso more naturally. Onboard sensors record force and ring-motion data, which are transmitted to a microcomputer that monitored and adjusted the brace. 

Unfortunately, RoSE had some shortcomings. Its rigid linear actuators had problems with shock loads from sudden movements and casual impacts with walls, doors, and furniture. Second, its motors were always on in order to apply force to the spine. Those motors also required heavy batteries that limited operating time.

These issues prompted Agrawal and two doctoral students, Chawin Ophaswongse and Rosemarie Murray, to design a better actuator. The result solves both the power and shock load issues by incorporating springs into the linear actuators.

In earlier RoSE prototypes, each motor drove a linear actuator that changed the position of an adjacent ring and determined its stiffness. The motor, linear actuator, and rings were rigidly attached in a series.

The new design includes a linear spring inside each actuator, so that movements of the actuator also apply and release force on the spring. One immediate benefit is that the compliant spring functions as a shock absorber if the robot accidentally hits something, protecting the exoskeleton.

It also turns out, thanks to the team’s modeling, that it is easier to control actuator output forces by using the springs to provide a further layer of sensor data. Measurements of each spring’s length are transmitted to an onboard microcomputer, whose algorithm calculates the forces and orientations of each ring in real time. The microcomputer sends instructions to the controller, which can more precisely and adaptively increase or lessen ring stiffness and orientation.

The motors in this system provide variable instead of continuous pressure, which lowers energy use and could allow the system to use smaller batteries.  

“With six springs in a three-ring device, you will have a six-dimensional springiness or stiffness at the cross-section level,” says Agrawal. “You can target and adjust corrective pressure on the torso that is adapted to each user’s spine condition. If the wearer has an unusual curvature in a certain direction you can stiffen in that direction.”

Agrawal anticipates that springs will be added to actuators in future generations of RoSE, allowing young people with scoliosis to stretch and flex more naturally as they grow and change.    

“The robotic devices that interact with humans must be softer and more compliant, and with this design, we can help users with a novel application to correct the upper body and modulate posture,” he says.

John Tibbetts is an independent writer.

Read more about robotics on AABME.org.