E xten d in g th e R e a ch of a Rod In je c te d Into a C y lin d e r T h ro u g h D is trib u te d V ib ra tio n Jahir PabonWe present results o f an experimental investigation o f a new mechanism for extending the reach o f an elastic rod injected into a horizontal cylindrical constraint, prior to the onset o f helical buckling. This is accomplished through distributed, vertical vibration o f the con straint during injection. A model system is developed that allows us to quantify the critical loads and resulting length scales o f the buckling configurations, while providing direct access to the buckling process through digital imaging. In the static case (no vibration), we vary the radial size o f the cylindrical constraint and find that our experimental results are in good agreement with existing predictions on the critical injection force and length o f injected rod fo r helical buckling. When vertical vibration is introduced, reach can be extended by up to a factor o f four, when compared to the static case. The injection speed (below a critical value that we uncover), as well as the amplitude and frequency o f vibration, are studied systematically and found to have an effect on the extent o f improvement attained.
We investigate continuous axial rotation as a mechanism for extending the reach of an elastic rod injected into a horizontal cylindrical constraint, prior to the onset of helical buckling. Our approach focuses on the development of precision desktop experiments to allow for a systematic investigation of three parameters that affect helical buckling: rod rotation speed, rod injection speed, and cylindrical constraint diameter. Within the parameter region explored, we found that the presence of axial rotation increases horizontal reach by as much as a factor of 5, when compared to the nonrotating case. In addition, we develop an experimentally validated theory that takes into account anisotropic friction and torsional effects. Our theoretical predictions are found to be in good agreement with experiments, and our results demonstrate the benefits of using axial rotation for extending reach of a rod injected into a constraining pipe.
Improved walking comfort has been linked with better bio-mimicking of the prosthetic ankle. This study investigated if a hydraulic ankle/foot can provide enough motion in both the sagit-tal and frontal planes during level and camber walking and if the hydraulic ankle/foot better mimics the biological ankle moment pattern compared with a fixed ankle/foot device. Five active male unilateral trans-femoral amputees performed level ground walking at normal and fast speeds and 2.5˚camber5˚camber walking in both directions using their own prostheses fitted with an "Echelon" hydraulic ankle/foot and an "Esprit" fixed ankle/foot. Ankle angles and the Trend Symmetry Index of the ankle moments were compared between prostheses and walking conditions. Significant differences between prostheses were found in the stance plantarflexion and dorsiflexion peaks with a greater range of motion being reached with the Echelon foot. The Echelon foot also showed significantly improved bio-mimicry of the ankle resistance moment in all walking conditions, either compared with the intact side of the same subject or with the "normal" mean curve from non-amputees. During camber walking, both types of ankle/foot devices showed similar changes in the frontal plane ankle angles. Results from a questionnaire showed the subjects were more satisfied with Echelon foot.
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