Design, development and testing of an adjustable above-knee prosthetic leg for toddlers.

[摘要] ENGLISH ABSTRACT: The aim of this research was to design and develop an above-knee lower limbprosthetic that can be adjusted to facilitate the growth of a child for a duration of three-years, between the ages of three and five years. The lower age limit is selected to accommodate for the occurrence of a mature gait pattern.Engineering requirements include a low-cost design and adjustability with respect to height, foot length and stiffness of the components. All requirementswere met. Design parameters were then determined to ensure a natural gait.Concept designs were rated according to their respective design parameters so that a final design could be chosen.The final design is lightweight, weighing 933 g (excluding a socket and foot cover). A low prototype cost of only R21 458 (Aug 2017) is incurred. The design consists of an ankle and foot prosthetic that is a single-axis, hinge-joint with a torsion spring of stiffness 808.59 Nmm/ which simulates the ankle stiffness and a removable footplate allowing for foot length adjustment. The pyloncomponent of the prosthetic consists of two overlapping tubes, constrained by a clamp to allow for a height adjustment of 45 mm. The knee component consistsof an Automatic Stance Phase Lock (ASPL) mechanism with an extension assist spring to allow for swing phase control. This design allows for the replacement ofthe spring of 3.34 N/mm to adjust the swing speed. The overall knee flexion is 67.3 , which is large enough to allow for adequate toe clearance. The overalldesign uses standard paediatric adapters, thus ensuring compatibility with other prosthetics.To evaluate the functionality of the prosthetic device, prior to testing with children, a gait emulator was designed. This emulator controls a linear actuatoremulating vertical excursion of the hip during swing-phase; a rotary actuator emulating the extension and flexion angles of the hip, and the use of a Bertectreadmill to emulate the horizontal motion of gait. Due to microcontroller timing limitations, the gait emulator did not allow for sufficient movement to occurduring toe-off, thus preventing the knee from unlocking and the ankle flexing.When adjustments in height or foot length were made no changes in the gait kinematics occurred as is evident from the standard deviation for each age rangebeing smaller than 2.1 . It was noted that an extension assist spring of a lower stiffness, 2.416 N/mm, resulted in the lowest standard deviation of the knee angle at only 0.76 . This was likely due to the low weight of the prosthetic limb during emulation. It is recommended that a spring with a lower stiffness be used for lighter individuals.Though sufficient moment could not be applied during the emulation, it can bespeculated that the knee can unlock and lock accurately via manual tests. Inconclusion, this prosthetic is entirely adjustable to facilitate three-year growth ofa child, between the ages of three to five years for a three year lifespan.

[发布机构] Stellenbosch University