Computational analysis of a theorised tendon-based trunk support device

Abstract

Introduction: Movement disorders, such as Cerebral Palsy, prevent children from fully developing their motor coordination abilities reducing their quality of life. Trunk control is a core coordination competency but there is limited variety in sitting based therapies. This paper investigates a theorised trunk support device for children which uses a system of elastic ropes and pulleys to support and prevent them from falling whilst they perform trunk control training exercises in a seated position. The aim of this study is to understand the mechanical properties required to ensure this device behaves safely and predictably. The device is considered safe if it prevents the child from falling and predictable if it always pulls the child towards an upright seating position. Additionally, it was investigated if the mechanical properties could be satisfied by off-the-shelf components and two possible pulley systems were compared.

Methods: To theoretically test if this device concept could meet the three criteria, a MATLAB simulation was written. A genetic optimization was then used to find the least stringent mechanical properties that still satisfy the three criteria. Off-the-shelf components that satisfy the mechanical properties were then found.

Results: Both pulley systems satisfied the safety and predictability criteria. Moreover, the necessary mechanical properties could be satisfied by off-the-shelf components, though some design modifications may be required. Ultimately, the configuration involving shorter ropes was determined to be the better option as it had less stringent mechanical requirements and potential design modifications would likely be easier to implement.

Conclusion: This study concluded that the optimised device, theoretically, shows good performance and seems practical to build. Future work is required to design a harness that would allow a child to comfortably train with the device.