Introduction: 3D Printed Pneumatic Logic Gates

This is a follow on from my first instructable: Pneumatic Logic Gates Made With Simple Tools

The last one didnt require much tools, this one however, will requre an SLA printer and optionally a laser cutter.

The design of the internals of the chip hasn't changed since my last instructable, this is just a more precise way of manufacturing one. I recommend to look at my previous instructable for explantion of how it works and how to use it.

Step 1: ​Required Tool/Materials

Materials:

  • 2 M3 screws and nuts, nylon preferred as to lower the chance of parts cracking
  • Mold making/cast able Silicone (a.k.a PDMS) - 1:1 part A to Part B mix ratio preferred, easier to measure at small amounts. I used Transparent Silicone Moulding Rubber (shore hardness A28)
  • 3mm thick transparent acrylic sheet.
  • A sealant, I used "Impex Original Hi Tack All Purpose Glue"
  • Wooden skewer
  • Masking tape

Tools:

  • Laser cutter (a saw can be used instead to cut the acrylic)
  • SLA printer, I used the Form 1+with Grey V3 resin for the top lid, and a KLD1260 with transparent resin for the bottom lid and mold.
  • Scissors
  • Craft knife / a ball needle sharpened with a drillbit

Step 2: SLA Printing

The top lid was printed at an angle as shown, on the Form 1+, a .FORM file is also included. The layer height was 0.05mm.

The mold and bottom lid was printed flat on the build plate on the KLD1260 (which uses a teflon film, as oposed to PDMS like on the Form 1+). A print oriented this way failed on the Form 1+, it stuck to the PDMS too well and came off the build plate.

If the holes in the top and bottom plate are not wide enough to fit the M3 screws, take a 3mm drill bit and widen it by hand (the resin is very brittle). Another way to solve this problem would be to adjust the hole size in the STL file.

Step 3: Cut Acrylic Plates

Cut a 29 by 27mm rectangle out of 3mm thick acrylic. (If you dont have a laser cutter, this can be done with a saw.) The STL file measures 30 by 27.5mm on the inside edge, but the plate shouldn't fit tightly.

Step 4: ​Cast Silicone

Equal weights of part A & B are measured out on a precision scale, a couple of grams is enough. The silicone is then degassed in a vacuum chamber to remove bubbles and put into the mold.

A good way to cast it is to put down a blob of silicone in the center of the mold and press down with the acrylic plate, making sure it flows to every corner.

Once the silicone has set, the excess around the edges is trimmed off with scissors.

Punch 2 holes in the silicone with a craft knife or sharpened ball needle as shown (needle can be sharpened with a countersink tool).

Step 5: ​Assembly

In this step, I used Hi-Tack Glue to make the device air-tight.
Make sure every part is dust free by washing it with water and continuing after the parts are dry.

Cut out four 3 by 2mm rectangles out of masking tape (or slightly smaller, what’s important is they can’t be any bigger than 3 by 2) and stick them to the top lid where the membrane valves are going to be. Check they align with the membranes (this step is very fiddly, I might use a laser cutter for the tape in the future).

Apply a thin layer of glue to the lid with a wooden skewer, the tape should protect the areas where the membranes are going to be from glue. Use tweezers to peel off the tape and stick the top lid on. Orientation matters – the flat side of the silicone should be facing down and the 2 holes in the silicone should align with the 2 squares in the corners. Press down with a weight, the silicone facing down on a clean flat surface.

Once the glue is moderately dry (it turns from white to transparent), a thin film of glue is applied to the silicone on the surface which is going to be in contact with the bottom lid (no glue should get into the channels or on the membrane). The silicone is pressed against the bottom lid. Make sure the lid is the right way round, if the bumps in the lid don’t align with the indentations in the silicone without the edge sticking out, you should turn the lid 180 deg. This is then pressed together with a weight on the lid and the silicone on a clean flat surface.

Once the 2nd layer of glue has dried, put in 2 nylon screws and nuts into the holes on the sides and tighten them evenly to stop the chip falling apart, not too tightly as to not bend the lids too much.

Step 6: D Latch

I made another microfluidic logic chip - a D latch that can be chained together to form a shift register. The same procedure is used to create it as the first chip, just with different STL files.

37 by 27.25mm, 3mm thick acrylic rectangle is needed for the mold.

Holes are punched into the silicone as shown.

The design work in theory, but there is a much higher chance of a leak forming, I only got the correct signal from output D and not D', meaning it cant yet send a signal to other latches.

Comments

author
novelchip (author)2017-08-12

About the latch circuit besides possible leaks you might consider to insert more resistive feedback channels in the loop since i also could not get it to work unless the feedback loop introduces a sufficient delay as i mentioned previosly. Adding resistance or capacitance in the feedback loop made it work for me and i could cascade several cpl latch curcuits.

author
dAcid (author)novelchip2017-08-13

Thanks for the advice.

I found footage of a braille display based an a fluidic shift register https://www.youtube.com/watch?v=7A9vwt2aj5Y

author
novelchip (author)2017-08-12

Wow! Well done! I like in particular your way to cast the silicone microfluidic layer and will certainly try to replicate the idea using my cnc mill to make such a mold. One question: how well does the glue stick to the silicone. I thought it us hard to glue silicone to a surface.

author
dAcid (author)novelchip2017-08-12

It works less as a glue and more as a sealant, it take very little force to peel the layers apart, but it's good enough. I could try using Silpoxy in the future

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