Three-dimensional pressure measurement by Alphafit.
>> http://www.alpha-fit.de/en/technology.html

Stretch pressure matrix for medical purposes.
>> http://vista-medical.com/subsite/stretch.php

Ready-made fabric touchpad from Plug and Wear!
>> http://www.plugandwear.com/default.asp?mod=product&cat_id=86&product_id=239

PPS pressure sensors.
>> http://www.pressureprofile.com/products.php

rSkin featured on blog >> http://revoltlab.com/2012/02/15/robotic-skin/

– pressure
– location
– 1 layer of fabric, stitches on either side
– rows, columns
– multi-touch
– pressure
Front and back:

Teensy:

Visualization written in Max/MSP:

Video
link >> http://youtu.be/ah8FhCbhDZw

Photos of similar setup that does not work well. Adrian says: “My intuition is that the thread can relax and the lack of pretension makes the results noisy and inconsistent.”

Fabric Touchpad

– pressure
– location
– 3 layers
– 4 connections
– single-touch
– pressure

CNMAT papers:
>> http://cnmat.berkeley.edu/publication/support_vector_machine_learning_gesture_signal_estimation_piezo_r
>> http://cnmat.berkeley.edu/system/files/attachments/optreallyfinalnime2011multitouch.pdf

Front and back

Video
link >> http://youtu.be/gPYyuuL-o7k

Thin, Strong, Solderable Conductive Thread

Goal Positioning

Colour Visualization and Moving Arm

Casting Eco-Flex silicone into mold. I mixed 7oz (3.5A:3.5B) of Eco Flex to fill the mold. It normally takes 4 hours to cure, but because it was so cold in my studio it took twice as long (i left it overnight, so maybe it even took longer).

Removing cured silicone from mold. The inside of the cast silicone is shaped by the aluminum foil wrapped around the arm, so there is not so much detail. The cast flesh would fit better if this was done better.

The result is a very squishy layer of silicone that i think will work really well to create a more uniform buffer layer between sensitive skin and hard robot arm. It might also have its downsides, as pressuring in any one point will automatically affect surrounding sensors, as they will be stretched into the indentation of the pressure point.

Video

Hiding what does not exist

Not all rows and columns intersect, a simple masking of the visualization hides what we should not see, but really i should find a more elegant solution.

Video

Circle Visualization

After realizing that the gray-scale visualization doesn’t show up well on video i decided to draw circles instead, their diameter increases with the increase of the sensor value. When i switched from doing the gray-scale to the circle i noticed that the frame-rate improved greatly (though there are still some delay issues, that i have not figured out yet). While the rows and columns are mapped correctly in this visualization, i am not accounting for areas on the hand which the grid does not cover. I have since done so and you can see some screen/shots above. When you watch the video, you might notice how when i am only pressuring the arm in one point, other readings are being affected, this is because it is impossible to pressure the arm in one point without applying counter-pressure elsewhere. And, because the hard arm itself does not have a uniform surface the counter pressure points are often in specific places. Also, pressuring the skin in a point that does not have a hard piece of arm directly behind it, causes the pressure applied to that point to spread to the surrounding area, since that is being stretched.

The following two screen-shots show the relaxed and then squeezed state of the rSkin.

Video
While the auto white-balance effect is better with this visualization, it still has some effect since the overall black/white ratio is changing.

Gray-scale Visualization

This visualization was very noticeably slower, the larger i made the application’s window size. At a window size of over 1200 width, the visualization was a few seconds behind real-time. I am not quite sure why this would be… but drawing circles (see above) helped solve that issue.

Video
Hard to show on video because my camera constantly adjusts its white balance when the balance of the screen changes. So what you see on video is often very different from what is really showing.

Video

Plugging Flesh and Skin Connections

Adjusting Pull-Down Resistors

All three layers

Sewing missing connections between columns on hand

PCB Board Layout

Before autorouting…

Machine Sewable Hard/Soft Connections

Using fusible interfacing to connect conductive fabric strips to perforated circuit board. Sewing with top conductive thread to fabric breakouts and soldering wires to perfboard.

Using zigzag stitch on sewing machine to sew top conductive thread over stripped ribbon cable wires.

Sewing to Plug and Wear’s knit breadboard fabric (right: with top thread conductive, left: with bottom thread conductive) and then soldering wires to the breadboard traces which are very thin wires.

I tried fixing my bit-shifting code, but also came across some different solutions:
Tom Igoe uses the Arduino bitRead() function >> http://www.tigoe.net/pcomp/code/arduinowiring/540
Buildr uses a two-dimensional array >> http://bildr.org/2011/02/cd74hc4067-arduino/
And others use bit-shifting code >> http://arduino.cc/en/Reference/Bitshift

I ended up implementing a two-dimensional array to store and retrieve the control pin combination values.
Here is are the code examples i used in the following video:
Arduino code >> http://web.media.mit.edu/~plusea/downloads/code/a_rSkin2Multi16.zip
Processing code >> http://web.media.mit.edu/~plusea/downloads/code/p_rSkin_11x11.zip

Video
Note that the sensor data from this test setup is quite noisy and too sensitive. This is because the conductive rows and columns are made using strips of conductive fabric, rather than conductive thread as in the final prototype. The video shows: 1) Individual sensor layers disconnected for testing individual (digital) row/column connections. 2) Data stream. 3) Turning the pull-down resistor. 4) Sensor readings with Velostat in between. The Velostat seems to be providing much cleaner values that the Eeontex fabric. This will be something to look into, because in initial (flat) prototypes the piezoresistive stretch fabrics fared better.

Download Arduino >> http://arduino.cc/en/Main/Software
Download Processing >> http://processing.org/download/

Download Arduino code >> http://web.media.mit.edu/~plusea/downloads/code/robotskin_a_4multi16channel.zip
Download Processing code >> http://web.media.mit.edu/~plusea/downloads/code/robotskin_p_4multi16channel.zip

Programming the Teensy using Arduino >> http://www.kobakant.at/DIY/?p=2497
Teensy Loader >> http://www.pjrc.com/teensy/loader.html
Teensyduino library >> http://www.pjrc.com/teensy/teensyduino.html
Teensy circuit diagram for Arduino programming:

Download stencil file (Adobe Illustrator) >> http://web.media.mit.edu/~plusea/downloads/RobotSkinStencils.ai.zip

Snap-shot of setup.

How connections should go:

Breadboarding the circuit.

Scaling up the electronics
The Mux (48 inputs) >> http://arduinoshield.net/shields/the-mux-multiplexer-shield-no-more-io-shortages
Mux Shield >> http://www.sparkfun.com/products/9832
Multiplexer shield (plus 16 inputs) >> http://www.thingiverse.com/thing:4128
Parallel to Serial Shifting (plus eight inputs) >> http://www.arduino.cc/en/Tutorial/ShiftIn

The arm with cables from various angles

All three layers: Flesh, piezoresistive, skin

Video

Pink flesh (columns)

White skin (rows)

Video of the making-of process

Isolating and protecting hard/soft connections with stretchy fabric glue and Smooth-on Ecoflex. Ecoflex is better.

Isolating ends of threads to keep them from fraying.

Sewing conductive traces with machine and by hand

Transferring stencil details.

Making stencils and transferring them.

Prototype circuitry, using one 16-channel multiplexer and 11 input pins on Arduino.

Looks awkward because outer skin layer is not a tight as it should be. 11 pin connector.

Sewn together.

Insulating and protecting with glue.

Layers.

Outer skin layer connections all come back to armpit.

Checking for unwanted connections

Sewing to perfboard, instead of soldering to wires.

Nope, soldering connections to super thin wires is not going to work. The wires are too fragile and so are the solder connections.

Stretchy traces on neoprene, flesh.

Stretchy ca. 4mm wide conductive traces on double knit skin.

Stretchy trace samples on neoprene and double knit.

Progress.

Edited skin, fits much better.

Editing skin to fit better.

Skin on top of flesh.

Only skin.

Only flesh.

Flesh and skin can stretch all the way over hand as well.

Getting dressed. Stretched skin.

Possible ways of connecting or stretching skin/flesh across limb.

Skin grid.