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Session: Neuromuscular – upper extremities
Session starts: Friday 25 January, 10:30
Presentation starts: 10:30
Room: Lecture room 535

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Ronald Bos (Delft University of Technology)
Dick Plettenburg (Delft University of Technology)

Abstract:
A lot of knowledge is available on hydraulics, where applications can range from micro-scale lab-on-chips to large-scale construction equipment. In between these two scales lies the millimeter-range of applications and is not explored as much. The goal of this study is to analyze whether this scale (miniature hydraulics) can be an interesting method of actuation in prosthetics, orthotics and other robotic applications, and how dimensional scaling of this method can be leveraged. In order to assess the state-of-the-art of miniature hydraulics, both miniature pneumatic and hydraulic actuators were searched in scientific literature due to their similar working principles. Additionally, products from Festo, SMC, Parker and Airpot were also scanned for actuators that fall within the miniature scale (<20 mm). Using performance indices that were normalized to scale [1], their performance relating to stroke and output force were assessed. The most suitable type of actuator for prosthetic and orthotic applications was further examined. A total of 39 different actuators were found originating from 18 scientific articles and 7 product lines from industry. Piston-type actuators with a contact seal (e.g., O-rings) were most suitable for prosthetic and orthotic applications due to their large relative strokes, high attainable pressures and a force output that is independent on stroke position. Only 9 actuators were hydraulic, which showed little difference in performance with pneumatic actuators of similar type. This is mostly because the working pressures were similar as well (<1.7 MPa), whereas hydraulic actuators have the potential to function at much higher pressures [2]. In fact, if miniaturization is coupled with an increase in pressure to reach a desired output force, efficiency is able to increase for smaller diameters. From these results, it can be concluded that piston-type actuators with O-ring seals are the most suitable method of miniature hydraulic actuation in applications that require high forces and strokes in small volumes. However, the state-of-the-art of miniature hydraulics can benefit from much higher pressures (>2 MPa) to achieve higher efficiencies. [1] Huber, J. E., Fleck, N. a., & Ashby, M. F. (1997). The selection of mechanical actuators based on performance indices. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 453(1965), 2185–2205. [2] Xia, J., & Durfee, W. K. (2013). Analysis of Small-Scale Hydraulic Actuation Systems. Journal of Mechanical Design, 135(9), 091001.