Tactile illusion via tangential skin strain

Implementation of the tactile illusion described in the following publication:

Masashi Nakatani, Akihiro Sato, Susumu Tachi, Vincent Hayward. Tactile illusion caused by tangential skin strain and analysis in terms of skin deformation. Proceedings of Eurohaptics 2008, LNCS 5024, Springer-Verlag, pp. 229-237.

You can download the scientific article here:

https://www.researchgate.net/publication/221011688_Tactile_Illusion_Caused_by_Tangential_Skin_Strain_and_Analysis_in_Terms_of_Skin_Deformation

I have attached Figure 1 from the article, where it explains how the illusion works. Do the following:

1) insert the protruding element into the receiving element;

2) place your index fingertip on the rugged region in the middle, while holding the non-rugged square nearer to you with your thumb and middle fingers;

3) slide the element further from you back and forth, using your other hand.

As you do this, you should feel either a bump or a groove under your index finger, depending on which element is oriented towards you and which one is oriented away from you. This means that, if you feel a bump, you should then be able to rotate the device by 180 degrees so that you are now sliding the other element, and you should feel a groove. Try it!

I printed this object using a Flashforge Finder with a 1.75mm filament at a resolution such that it took about 2 hours to complete the job. Extruder temperature was near 210 deg C. You should use a resolution that is sufficient to render the rugged region in the middle of the device adequately. The object is designed to be printed at a magnification such that its shorter side is 30mm. I have played around with the size of the protruding element to ensure that it would snugly fit into the receiving element, at least for the printing specifications I used. It is important that the fit is snug in order to obtain a good illusion.