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Design, build and test an assistive lower limb exoskeleton
Author(s)
Mukengere, Musimwa Valery
Date Issued
2026
Type
master thesis
Publisher
Cape Peninsula University of Technology
Abstract
In 2017, the global elderly population was approximately 962 million, and this figure is projected to reach 2.1 billion by 2050, according to the United Nations. Africa is anticipated to experience an increase of 225.8 million elderly people during the same period. As of 2019, South Africa's elderly population stood at 5.3 million, and this number is expected to continue growing, according to Statistics South Africa. In recent years, exoskeletons have emerged as a significant technological advancement to assist individuals with limb disabilities. However, many existing LLEs tend to be heavy and cumbersome, thereby increasing the user's metabolic cost. The objective of this study is to design an adjustable, lightweight LLE that enhances the mobility of elderly users by reducing their metabolic expenditure. This LLE is specifically designed for movement in the sagittal plane; therefore, it is assumed that users will rely on crutches for additional lateral support and balance, as the exoskeleton is limited to forward motion. The development of this walking robot was achieved using CAD software to model the LLE. During the modelling process, anthropometric data were used to shape the design of the LLE in relation to its intended user. The LLE was specifically designed to accommodate users ranging from 1.505 m to 1.740 m tall, with a maximum weight of 80 kg. After completing the modelling phase, the LLE was imported into Ansys for finite element analysis (FEA), which was conducted segment by segment. Upon confirming the structural integrity of the LLE frame, the walking robot was imported into MATLAB. An adaptation of the walking algorithm developed by Castro and Kim in MATLAB was modified to align with the LLE's design requirements for this research. During this phase, both kinematic and dynamic modelling were established, along with the Linear Inverted Pendulum Model, which was essential for the LLE's walking functionality. The weight of the LLE frame was measured at 4.942 kg; however, with the actuators included, the total weight rose to 13.338 kg, excluding the 16 kg of the two batteries. FEA results for the LLE frame demonstrated its ability to endure the applied loads without compromising its structural integrity. The yield strength for each segment was maintained below those of aluminium 6061-T6 and 6082-T6 for the frame, and below that of low-carbon steel for the bolts and nuts. Furthermore, the buckling load for each segment of the LLE remained below the critical buckling load during the stance phase, whereas the maximum bending stress experienced by these segments stayed below the specified permissible bending stress during the swing phase. In a MATLAB simulation, the LLE successfully walked 5.63 metres in 10 seconds, demonstrating its responsiveness to the walking algorithm. The scaled-down prototype of the LLE effectively mirrored the walking gait cycle in practice, with results from both the experiment and the simulations closely aligning. The contribution of this research is centred on the development of the LLE design to assist the elderly population by improving their walking capabilities, which are affected by aging.
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Mukengere, MV_212303015 (1).pdf
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13.44 MB
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