University of Twente Student Theses


The development of a cable-driven variable stiffness mechanism test bed

Manourat, Norrasaet (2019) The development of a cable-driven variable stiffness mechanism test bed.

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Abstract:A variable stiffness actuator contributes an interaction with uncertain environment together with substantial robustness of mechanism while a conventional actuator could not carry out. With these benefits, variable stiffness actuators have become an alternative for diverse applications particularly in the field of biorobotics. One design which is usually applied for imitating physiological movement is an antagonistic mechanism. However, bulkiness is a common constraint for the currently used VSA in biorobotics. To reduce size and weight, the cable-driven mechanism has been introduced.The primary goal of this project was to utilize the assistive arm-support exoskeleton, and to that end, both mechanisms have been integrated, proposing a novel cable driven VSA mechanism. In this study, the development of a cable-driven variable stiffness mechanism test bed is presented. The mechanism is introduced with the cable-driven antagonistic mechanism providing a change of stiffness without varying torque. Variation of stiffness is conducted by a cable-driven system, controlling the pretension of elastic elements which work antagonistically resulting in an equilibrium position. A methodology of design is given along with a primary mathematical model, prototyping and testing. Measurements performed with the test bed show the validity of the theoretical findings, the outcomes satisfy the primary objectives. The stiffness is adaptable with a range of 1.13 Nm/rad to 1.64 Nm/rad. It also brings a constant torque while modulating the stiffness, the measured output displacement for static and dynamic measurement exhibit less than 0.0016 rad and 0.0033 rad, respectively when the stiffness changed by 45.13 %. Moreover, stiffness modulation seems to be qualitatively and quantitatively identical between measurement and simulation (with mean absolute error range of 0.2779 - 0.3355 Nm). Promising results show the possibilities of future work on developing cable-driven variable stiffness actuators by adopting the redesigned this mechanism and applying the actuator to wearable robotic applications.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:52 mechanical engineering
Programme:Biomedical Engineering MSc (66226)
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