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Redesign of the MASMini

Etxeberria Echávarri, A. (2018) Redesign of the MASMini.

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Abstract:Gravity compensation arm supports are being more and more used for compensating the muscle weakness of patients, not only while the rehabilitation time but also during the activities of daily living. Among these devices there is the Saebo MASMini developed by Hankamp Rehab. The aim of this report is to make this arm support cheaper so it can be affordable for more patients to have it and be able to use it at home. For that, the principal mechanism, which allows to adjust the mass compensation according to each user, has been redesigned. The mechanism of the gravity compensation uses a spring pulley system. To hold the equilibrium of the gravity equilibrator this equation should be followed: MgL=akr. Where M refers to the arm mass, g to the gravity constant, L to the length of the last link of the arm support, k to the stiffness of the spring and a and r to distances from the pivoting point of the arm support. To compensate the mass, one of the distances a or r can be modified and that is what has been developed for redesigning this mechanism. Using the same spring system as the MASMini, and for a range of mass compensation from 1.06kg ¬¬to 4.18kg, distance a has been fixed to 20mm and it has been obtained a range of distance r from 21.5mm to 84.5mm. In this case, the distance r can be adjusted thanks to a teeth shape design where the shaft stopping at each point can be manually moved by a hand holder. In conclusion, this design results cheaper than the actual MASMini and can potentially be cheaper by changing to a simpler design of some parts. However, it should be considered that only the main mechanism has been analyzed here and that the new links connecting the elbow support must be added.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Programme:Mechanical Engineering MSc (60439)
Keywords:arm support, mass compensation, spring, gravity
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