Capacitive Touch Screen Typing Splint

Not all assistive devices need to be complicated, bulky or awkward. It is possible to make highly functional assistive devices that are simple, lightweight, and elegantly designed.

One of the first things I designed to 3D print was a typing splint for touch screens for people with limited use of their hands. I've always had to hand make each one based on the needs of the individual, but the 3D printer gave us the ability to create models that could be scaled and skewed to quickly fit the needs of the individual. It is also beneficial to have an easy way to replace broken or lost devices, and because I posted the designs for free, any school or other people with access to a 3D printer could make on an as-needed basis without having to ask me.

Supplies:

Thingiverse Free 3D printable assistive technology models:
http://www.accesswoodworx.com/thingiverse

Scotch-Brite Non-Scratch Scrub Sponge (for iPhone and Android!) http://www.accesswoodworx.com/scotchbrite

Proto-pasta CDP12805 Composite Conductive PLA, 2.85 mm 500 g http://www.accesswoodworx.com/protopasta2_85mm

Proto-pasta CDP11705 Composite Conductive PLA, 1.75 mm 500 g http://www.accesswoodworx.com/protopasta1_75mm

Heat Gun (NOT a hairdryer)
http://www.accesswoodworx.com/heatgun

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Step 1: ​Download 3D Model

Download the stereolithographic file (.STL) from the Thingiverse website. You can go to Thingiverse and search for "touchscreen typing cuff stylus", or just click on the following link:

https://www.thingiverse.com/thing:1315004

Step 2: Load 3D Model Into Slicer Program

Once you have the 3D model file, open it in your slicing program. We use the Lulzbot edition of Cura because we have a Taz 5 at the rehab engineering workshop, but you can use whatever slicer you like.

You can scale the model based on your needs, and arrange it on your build plate how it will print best.

Step 3: Prepare Your Printer

If you expect to use this typing splint with a touch screen, you will need a conductive print filament. We use Protopasta conductive PLA. The printer in the rehab engineering workshop has a 3 mm nozzle, but we have some with 1.75mm nozzles in other locations.

Here are links to the filament we use:

Proto-pasta CDP12805 Composite Conductive PLA, 2.85 mm 500 g
http://www.accesswoodworx.com/protopasta2_85mm

Proto-pasta CDP11705 Composite Conductive PLA, 1.75 mm 500 g http://www.accesswoodworx.com/protopasta1_75mm

In case you are currious, the electrical specs of the filament are:

  • Volume resistivity of molded resin (not 3D Printed): 15 ohm-cm
  • Volume resistivity of 3D printed parts along layers (x/y): 30 ohm-cm
  • Volume resistivity of 3D printed parts against layers (z): 115 ohm-cm
  • Resistance of a 10cm length of 1.75mm filament: 2-3kohm
  • Resistance of a 10cm length of 2.85mm filament: 800-1200ohm

Load the filament in your printer, and be sure to set your print head and bed temperatures for the PLA.

Lulzbot recommends the following temperature settings:

  • Extruder: 215°C
  • Bed: 60°C
  • Part Removal: 50°C

However, I have found that we need to use higher temperatures on the Taz 5 with the Flexi Duali print head in our local rehab engineering workshop.

  • Our Extruder: 230°C
  • Our Print Bed: 110°C
  • Part Removal: 60°C

Step 4: Click Print and Pray

Even after years of printing stuff we still have to pray a bit when we first try and print a part. As you can see in the photos, we have had more than our share of print failure.

It is always a good idea to monitor the first layer when printing. If the first layer completes without any issues, chances are your part will be fine. If there are any problems, such as a little bit not sticking, part of the layer not printing consistently, or things just not looking right you should stop and reset the print. Moving or rotating the part often will help.

When you return in 45 minutes you will either have a mess of melted plastic or a nicely printed part :)

Assuming you have a nicely printed part, remove if from the print bed.

Step 5: Form the Splint to Fit

Clean up the edges of the part with a knife or sandpaper.

Set up a heat gun, heat strip, hairdryer, or another concentrated source of heat to form the plastic. I don't recommend an open flame source.

Warning: A heat gun is not a hairdryer. DO NOT ATTEMPT DRY YOUR HAIR WITH IT!!!

Warm the areas that need to be bent and form around your hand or similar shaped form. PLA has a low melting point, but can still be uncomfortably hot to the touch, so if you want to form around your hand you may want to wear a thin protective glove.

Shape the hand cuff, finger cuff, and bend the stylus in whatever way you need to meet your needs.

Step 6: Experiment and Adjust

PLA is easy to reheat and reshape. I suggest trying out the typing splint and shaping it while using it. Shape it so that it works well for the position and angle the touch screen is normally located at.

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