Introduction

Falling is the leading cause of accident related injury among all age groups, but is particularly threatening among the elderly. A key factor leading to falls is degraded balance control. At the Biorobotics Lab of Delft University of Technology, a device is being developed that can actively assist in balancing persons.

Problem definition

Falling can have a significant psychological impact. The physical injury can be overwhelming, but also the loss of confidence after a bad fall can reduce mobility and lead to decreased independency in normal everyday life. In other words, people start dodging social and physical activities and are in need of more care.

At the DBL (Delft Biorobotics Lab) they have been constructing a backpack-like device that is able to support people with balancing problems and preventing them from taking a fall.

Approach

The backpack contains two actuators called “control moment gyroscopes”. Femto together with Hyperion Technologies assisted in creating the mechanical design and advanced non linear assessment of these gyroscopes.

Important conditions were being as lightweight as possible to carry comfortably, yet able to deliver temporarily a large enough force (in fact a moment) required to compensate for out-of-balance motion.

This required the flywheels in the gyroscopes to turn at extremely high turning speed, and a design that is optimized for maximum rotational inertia by placing weight as far as possible away from the rotation axle. The flywheels must be able to resist not only the large centrifugal load but also the out-of-balance compensation reaction loads that will be applied to the flywheel shafts. These actuator loads could be highly fatigue sensitive because of the fast turning speed (many cycles). An optimal wheel design was developed given these loads. The housing design (pressure vessel) and its lightest possible shape was also established given the vacuum-, impact-, and actuators loads applied to it. For safety reasons also impact acceleration in any direction was part of the design scope.

Conclusion

For the complete design, both static and dynamic (Advanced Nonlinear Transient by Femap with NX Nastran) FE simulations were carried out to prove its strength and behaviour and determine details like required bolts and pretension. In the end manufacturability and its costs also played an important part of the design. A prototype was made and tested at the DBL. For more information you can check out their website