Design of a hip orthosis that uses a compliant mechanism to correct Trendelenburg gait
S.V. Bosselaar (TU Delft - Mechanical Engineering)
Just Herder – Mentor (TU Delft - Mechatronic Systems Design)
Ron A.J. Van Ostayen – Graduation committee member (TU Delft - Mechatronic Systems Design)
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Abstract
Trendelenburg gait is an abnormal gait pattern caused by failure of the hip abduction mechanism. Under the external adduction moment caused by the body weight, this results in excessive adduction characterized by a drop of the pelvis on the contralateral side. Existing assistive devices are inadequate for this condition. Therefore, this thesis aimed to develop a hip orthosis that uses a compliant mechanism to correct Trendelenburg gait. Compared to traditional mechanisms, compliant mechanisms offer several advantages in orthotic applications, including compactness, low mass, adaptability to misalignment, and adjustable levels of support. However, despite these benefits being recognized, research on practical implementation remains limited.
The design process distinguished between the attachment parts and the mechanism of the orthosis. For the attachment parts, the goal was to evaluate whether the established orthotic methods and materials are suitable for this application. A preliminary design confirmed their suitability. For the mechanism, the goal was to develop an innovative compliant solution by either advancing previous work or introducing a new concept. The latter showed more potential for flexion stiffness minimization, as well as a lightweight and compact design and was therefore selected for further development.
Two mechanism design variations were developed: one using a conventional leaf flexure and one using a leaf flexure incorporating warping constraints. As anticipated, warping constraints enabled further reduction of the flexion stiffness. The hip flexion moment required to achieve a 30° flexion angle was 7.9 Nm in the design using a conventional leaf flexure, and 0.55 Nm in the design using a leaf flexure incorporating warping constraints. This result indicates the potential of warping constraints for broader implementation in compliant mechanisms to improve the ratio between lateral and bending stiffness in leaf flexures at large deflections. The main tradeoff for this improvement was increased mass, from 0.36 kg to 0.98 kg. Both designs provided sufficient adduction stiffness to constrain adduction under the adduction moment applied by the body weight, and are therefore effective in correcting Trendelenburg gait.
The resulting overall orthosis design is a promising solution, providing the foundation for future research to validate its technical and clinical performance and development into a usable product.