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Design of an Electro-Hydrostatic Actuated Ankle-Foot Orthosis

Jimenez, J.J. (2018) Design of an Electro-Hydrostatic Actuated Ankle-Foot Orthosis.

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Abstract:This report presents the development of a research tool for the Biomechanical Engineering (BME) department of the Universty of Twente. The main goal of the presented project is to develop an hydrostatic actuated ankle exoskeleton. A frontal actuated ankle exoskeleton with a passive return was designed. The device counted with two hydraulic cylinders to assist plantarflexion and two mechanical springs as return elements.Once finish the physical prototype was tested using two different platforms. One platform consisted of a testing leg with digital force and motion sensors, that was connected to a hydrostatic input stage. The other had a manual pump with a digital force an analog pressure sensor. Results obtained of the device’s range of motion (ROM) showed that it is capable of reaching approximately 80�of total ROM, from which a maximum dorsiflexion angle of 24�and a maximum plantarflexion angle of 56�is reached. Furthermore, while performing a maximum stress test, it was found that the device can withstand a maximum ankle torque of 115.9 Nm. In addition, the device was able to reach an ankle angular velocity of 113.16 deg/s. In total four of eight requirements set in this project were achieved. From this, the requirements that were not meet are the maximum exoskeleton weight, minimum actuation torque, minimum actuation velocity and the pain pressure threshold (PPT) for different areas of the lower limb. In particular, to reach the minimum actuation torques for the different human movements the device structural stability needs to be improved. In the case of the weight, it is expected that by doing an optimization for lighter and stronger materials the total device mass can be further reduced. Due to equipment limitations, (1) it was neither possible to prove if the device’s actuation can reach the minimum gait velocity requirements nor (2) if the device applied a significant pressure to the testing leg. Hence, to prove the speed and pressure requirements, it would be necessary to obtain small strain gauge sensors and a suitable input stage. In conclusion, the device presented in this report is a promising solution to increase the ROM found in common ankle exoskeleton designs and it is a valuable reference to create new and compact devices that are able to perform different human movements.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:52 mechanical engineering
Programme:Biomedical Engineering MSc (66226)
Link to this item:http://purl.utwente.nl/essays/77047
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