Enhancing Arm Mobility in the Compact X-Scissors Device (CXD) through Spring Integration using a Simulation-Driven Design approach

The Compact X-Scissors Device (CXD) is a passive device developed at Aalborg University (AAU) and integrated into a wearable orthosis provided by the startup company Liftya. It offers stability for patients with neuromuscular disorders or injuries but it does not support dynamic movement assistance. The goal of this thesis project is to improve mobility by modifying the CXD’s design incorporating springs to reduce the weight on the arm, making movement easier for the user. To achieve this goal a Simulation-Driven Design approach was adopted, integrating simulations throughout the design process to provide deeper insights and explore a wider range of design alternatives. The first step involved developing a musculoskeletal model that included the arm, torso, and CXD, using the AnyBody Modeling System Software. Leveraging the system’s features, and particularly its integration with Python via AnyPyTools, multiple Inverse Dynamics simulations were performed. These simulations enabled a thorough analysis of various arm movements relevant to Activities of Daily Living, helping to pinpoint optimal attachment points for potential springs designed to significantly reduce shoulder muscle effort. The simulations of the investigated movements provided the optimal attach- ment points and different stiffness values for the springs specific for the created model. Two springs were identified, each assisting the shoulder separately in flexion and abduction movements. When working together, they nearly eliminate shoulder effort during combined movements. Once the attachment points were identified, potential supports for the springs were proposed. SolidWorks software was used to create CAD models of these supports, which were designed to be positioned on the rigid links of the CXD. The advantages of the approach used include its cost-effectiveness and patient-specific nature, as it allows for the identification of optimal attachment points and spring stiffnesses tailored to each individual. Additionally, it eliminates the need for unnecessary experiments that may not meet the desired specifications. However, it is important to note that the results were derived from a simplified model that includes approximations compared to real-life conditions. In future work, the model could be enhanced by incorporating soft tissue, specific muscles, and ligaments. Furthermore, the stiffness of the identified springs is considerable, making them challenging to manufacture nd position. A more in-depth analysis of the lifecycle and stress conditions of the entire model, particularly regarding the spring supports, would also be necessary. With adequate financial resources, future efforts could explore the possibility of actively actuating the CXD, though this would increase the size of the device, potentially limiting its usability for patients. Additionally, incorporating active components would change the classification of the device, leading to delays and complications in bringing it to market.