Embedded Files
Integration of All Parts
Project Overview and Assembly
Balloon Test
Preparing the Prosthesis
Creating the Jamming Layer
Fabrication
Serpentine Spring Selection
Pattern Selection
Creating the Silicone Membranes
Second Iteration: Socket Pocket
First Iteration: Flat
Airtightness of the Integrated Membrane
3 Point Bending of Integrated Flat Membrane
3 Point Bending of the Empty Flat Membrane
Fabrication
Balloon Test:
This test uses a rubber balloon to simulate a 10% increase in the volume of residual limb, where a rubber balloon was inserted into the prosthesis and was gradually inflated with water. The FSR attached on the inner side of the socket pocket started to measure the contact pressure once the FSR started to have readings. The balloon was inflated to 110% of its starting volume to simulate a 10% volume increase of the prosthesis. This test was repeated three times for three vacuum pressures (101 kPa, 70 kPa, and 45 kPa absolute vacuum pressure) to evaluate the effectiveness of vacuuming on contact pressure.
20220308_164053.mp4Preparing the Prosthesis
Integrating the socket pocket into the prosthesis:
Attaching the integrated socket pocket to the cut-out with strips of PET and cyanoacrylate (Loctite 495 and activator)
Cutting a hole in the shape of the socket pocket membrane for attachment and smoothing it for better adhesion
Creating the Jamming Layer
Fabrication
Stretch_Hexagons.movDemonstration of Stretching of the Jamming Layer
Lasercutter.MOVLasercutting File.MOVJamming Layers were Laser-Cut from 0.005 inch thick PET Sheets
The 75% length spring (cut 75% of the width or vertical component of the rectangular area that contains the retracted serpentine spring) was chosen based on the fact that it has a high yield displacement while being able to maintain stiffness.
Serpentine Spring Size Selection
Two hexagons connected by a single spring of each length and of each thickness of PET (0.002 and 0.005 inch) are stretched until fracture with the Instron in order to obtain material properties
Internal Jamming Layer Pattern
Serpentine springs of different sizes connect hexagonal shapes
This geometry was selected because the hexagon shape allowed for the maximum overlap of jamming sheets when aligning the nodes of the hexagons for each layer, allowing for a higher softness/stiffness ratio and 3D deformations of a 2D plane without areas of high stress or plastic deformation.
12 layers were used for the flat membrane and 16 layers were used for the socket pocket. The numbers of layers was increased for the socket pocket in order to increase the maximum achievable stiffness.
The more layers, the more stiffness.
Creating the Silicone Membranes
Second Iteration: Socket Pocket
Socket Pocket geometry of silicone membrane fits the shape of the cut-out of the prosthesis
First Iteration: Flat Membrane
Flat geometry of the silicone membrane was made to practice and finalize the casting process as well as finalize the assembly process of the integrated membrane
Airtightness of Integrated Membrane
The airtightness was tested in many ways:
Dunk test (making sure there are no bubbles that escape)
Measuring leakage with a manual vacuum pump and a digital air pressure sensor
time for pressure to drop (no load).MOV
Leaking Results
~3 seconds active pumping every ~5 min
Maintain vacuum pressure of ±3 kPa around target (5% of working range)
~40-43 dB noise from pump operation
3 Point Bending Instron Testing of Integrated Membrane
Integrated Membrane:
Jamming layers inside the two sides of the membranes with a bag connector
Stiffness increased as pressure inside the membrane increased!
3 Point Bending Instron Testing of the Empty Flat Membrane
IMG_1062.movFabrication
Pour molding technique (pouring the Dragon Skin 10 MEDIUM silicone into the bottom mold, placing the top mold on, and then compressing them together with hardware) and a vacuum chamber was used to ensure there were no air bubbles in the membranes
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