The first piece is 4"by 4", but it can be made in larger pieces. Flexing it
dose's change its readings. A PIC16f877 is scanning and interpreting the
sense of touch. To compensate for flexing it over, various shapes, such as a
finger-hand. Once the skin is bent over the shape, I send a command via
rs232 to the PIC16f877 chip. The PIC16f877 chip scans all points on the skin
and saves baseline readings. Then when the skin touches something, linear
changes in the readings from the baseline readings are use to determine how
much force is at each point.
Dennis, Sounds very interesting. Do you have anything written up on it
that is viewable on the Web? I'd think a lot of people will be very keen
to try it out. You might become famous!
I don't have it on the web yet. Just in a notebook and assembler code on a
computer. I have a web site, presently used for a small business I started
several years ago. I have recently licensed the technology I was using for
my company to a large company that will be mass producing and mass
distributing my present products, starting in January. I plan to change my
web site into a robotics site and will place the skin on it. I'm planning on
using Visual basic to be able to map the pressure points on a bitmap image
with red for higher pressure points and blue for lower pressure points.
Presently the PIC16F877 is sending the data through an rs232 port in ASCII
format. I'm planning on changing to a USB port also, probably with a
PIC18F2455. Speaking of fame, I have your book Robot Builders Bonanza and
I had an idea to make robot skin out of "blister" type
keypads. These are the thin, flexible keypads used in
wet/dirty environments, or on cheap consumer electronic
equipment. I found a place in Shanghai that could
manufacture them for less than 10 cents per square inch,
and could put up to 25 blisters in a square inch. They
come with an adhesive peel-and-stick back.
2. Robust. Impervious to dirt, moisture.
3. Can bend around a cylinder less than 1" in diameter
4. Easy to interface to a CPU. The number of I/O pins
needed is 2*(sqrt of the number of pads), but you can
reduce that by using a multiplexer and/or demultiplexer.
1. Binary (off or on), does not measure degree of pressure
2. Resolution is "only" 0.2 inch
3. Can curve in only on direction (cylinder) not two (sphere).
4. Limitations on how it can be cut into different shapes.
I didn't go forward with the idea because the minimum order
quantity was too high (I think it was a hundred) and I only
needed a handful. But if others are interested, I could
revive the project. Let me know.
The two most commons ways seem to be scanning a matrix of switches (e.g.
a keyboard), or measuring the voltage through resistive foam. With the
former, you have no pressure sensitivity but can sense multiple
contacts. With the later, you can only sense one contact, but you have
pressure sensitivity. Of course, you could create a matrix of resistive
foam pads, but all the wiring quickly becomes far too labor intensive
for any usably large pieces of skin.
Could you elaborate on your design? What material did you use to
construct the skin?
I'm going theough the patent process at the moment, but it is simular to the
resistive method. It contains a matrix of 30 gauge wires and also has a
rubber outer layer and a foam inner layer. It can map multiple pressure
points at the same time and if 2 points are close together, can average the
two points to "esimate" pressure between the points. With a little more work
I should me able to map an image of the pressure points on a computer image.
Yes, I suppose you're right. If you put a diode at every junction in the
matrix, you could scan the resistive components the same you would with
normal on/off contacts. I believe this is the way a number of
researchers are planning on implementing "robot skin" with the recent
fabrication of flexible transistors.
Isn't this basically how a resistive touch screen works, though? One
difference in the touch screen could be that the membrane isn't
flexible, but that's not needed/desired in that application. It's
actually pretty hard to design a transparent substrate for a screen that
also has decent resolution. They've done pretty well with it, though
resistive screens block about 25% of the light.
On the latest touch screens they deduce pressure by the distribution of
the pattern (fingers flatten out; in robot skin the skin is compliant,
so it's the same effect but in reverse) and force can be deduced by the
timing relationships of the pattern. A sudden tap creates has a pattern
where all the points are produced nearly simultaneously, whereas in a
softer touch the pressure pattern is made over a period of a few more
Of course if you're applying for a patent you can't say anything now,
but I'd be be curious how this invention differs from resistive touch
At this point I can't say to much. When I get further in to the patent
proccess I will give more details. The skin uses a different technique then
the resistance type. It dos have a matrix of X/Y locations. A diode isn't
needed because if the skin is pressed at 2 different points both the X and Y
sense of touch detects then and can map there location and there pressure.
Dennis, this is totally off-topic, but how are you going about patenting
this idea? Have you hired a patent attorney or are you doing the
As with the others here, I can't wait to hear more about what you're
I'm going through an attorney. I've been through the patent proccess before
and I have 5 produces licensed by a large company. I don't trust myself to
do it right.I would like to put the skin on a web site before long with alot
more info. It's easy to make with materials from Lows and few electronics
parts.I think alot of robotist would enjoy working with it.
Hmm. How about putting a resistive foam pad under the matrix of
Is there any resistive foam made specifically for pressure sensing?
Or do you just use the stuff designed for storing ICs?
Is there a good way to sense a touch using piezo-electric sensors?
The problem with this is detecting multiple contacts. Simple switches
can be scanned in sequence, and their on/off state won't effect the
reading of other switches. However, if you replaced those switches with
variable resistances, the readings from multiple contacts would average
out and would be very difficult to make sense of. So in that case you'd
only be able to detect the X-Y coordinates of a single point of contact.
This is basically how resistive touch screens work, but that's probably
not what you're looking for. You could of course get around this by
creating a separate circuit for each sensor, but then the wiring becomes
unmaintainable and quickly drives you insane.
The foam used to store ICs is usually pretty hard to work with. However,
there are a few manufacturers who sell pressure activated rubber, like
Generally speaking, it can be difficult to measure static forces with
piezoelectric sensors, but some are working on it. Here's an interesting
paper on the design of a tactile sensor using piezoelectric resonance
However, I don't know of anyone who's made a commercial sensor using
Pressure sensitive resistors(such as foam) under a matrix of contacts
could be a usefull sensor, but resolving individual points could be non
trivial. Energising one row to scan while grounding all other rows
should help, but you'd still be reading row N against other rows.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.