Test the IR sensor to make sure it works without the silicone skin.
Super glue the flex circuit in place along the back side of the 3D printed support:
Put the IR sensor through it's hole before applying thin super glue or the sensor will get coated in glue when you push it through. Having a thin layer of glue over your sensor will make it much less sensitive!
We are using the EE-SY199 (Omron Corporation) emitter-detector pair.
Re-test your IR sensors to make sure they are all still sensitive enough.
Prime the 3D printed part for the silicone to stick:
Give the projet parts a good hot soak in isopropyl alcohol to get all the wax remnants off. I heat the alcohol in the oven with the parts in it after melting the wax. I let it sit for ~20 min. It will have a more opaque white surface finish afterward.
Roughen the bonding surface with sand paper.
Use RTV Primer and let part sit for 2+ hours.
Pour the thin layer of clear silicone (1mm thick):
7/9/2014: FAIL. Tried DragonSkin Fast (Shore A Hardness 10) but it was too viscous (23000 cps) to go into the 1mm crack or even squeezed out of a 20 gauge needle. This is like the material in the Lincoln, et al paper "An Optical 3D Force Sensor for Biomedical Devices" from 2012. One option is to use silicone thinner but this may be tricky and less controllable on a prototype-to-prototype basis. Or, a less viscous material could be used.
7/10/2014: SUCCESS. Tried EcoFlex 0030 (Shore OO Hardness 30) and I was able to use a 21 gauge syringe needle to get it into the crack (3000 cps). This is more like in the Sandia Hand that used Shore OO Hardness 10 silicone for the clear and white layers. Having a squishier layer of clear silicone will make the sensor more sensitive. I first degassed the silicone in the cup, then filled the cavity half way and degassed again. I degassed once more after filling it up all the way. Then I topped it off one last time. Wiped off the extra material with a paper towel.
De-mold the silicone layer... TBD
Pour the white reflective layer of silicone... TBD. Probably the same material as the clear layer.
Pour the black protective layer of silicone... TBD. A silicone that is resistance to tearing, either DragonSkin20 or a MoldMax. I may need to use the silicone thinner for this layer.