also: neoprene bend sensor, conductive thread Bend Sensor, Bend Sensor (thread)
This bend sensor actually reacts (decreases in resistance) to pressure, not specifically to bend. But because it is sandwiched between two layers of neoprene (rather sturdy fabric), pressure is exerted while bending, thus allowing one to measure bend (angle) via pressure.
>> Fabric Bend Sensor Instructable
>> Neoprene Bend Sensor IMPROVED Instructable
We find that this construction method gives good results (sensitivity) for measuring the bend of human joints when attached to the body. It is sensitive enough to register even slight bend and has a large enough range to still get information when the limbs are fully bent. The neoprene is great for isolating the conductive thread stitches and keeps the sensor from wrinkling even when repeatedly being bend.
The resistance range of this bend sensor depends a lot on the initial pressure. Ideally you have above 2M ohm resistance between both contacts when the sensor is lying flat and unattached. But this can vary, depending on how the sensor is sewn and how big the overlap of the adjacent conductive surfaces are. This is why i choose to sew the contacts as diagonal stitches of conductive thread – to minimize the overlap of conductive surface. But only the slightest bend or touch of the finger will generally bring the resistance down to a few Kilo ohm and, when fully pressured, it goes down to about 200 ohm. The sensor still detects a difference, right down to about as hard as you can press with your fingers. The range is non-linear and gets smaller as the resistance decreases.
How to make a fabric bend sensor
The following stencil is a good guide for building your first bend sensor. But the great thing about this design is that it is highly customizable. You can easily change the shape, size and some of the materials in this sensor to better suit your own project. For a more sensitive sensor increase size of the conductive surfaces on either side of the Velostat. The piezoresistive (pressure sensing) properties of Velostat work through the material and not across it, so your conductive surfaces need to overlap adjacently on either side of the Velostat. Reduce or increase the overlapping conductive surface by removing or adding more stitches or even by replacing the conductive thread by a piece of conductive fabric. Take note that the conductive stitches in the following stencil are designed so that they only overlap in one point, reducing the conductive surface overlap to an absolute minimum. But the sensor is still very sensitive. To some degree you can also control the sensitivity of the sensor by adding multiple layers of Velostat. How tight you stitch together your sensor also impacts the range it will be able to detect, as pressure coming from these stitches will eliminate part of your sensing spectrum.
>> Download Fabric Bend Sensor stencil (Old)
>> Download Neoprene Bend Sensor stencil (Newer)
Materials and Tools
Materials: Neoprene, conductive thread, stretch conductive fabric, velostat, fusible
Tools: Fabric scissors, fabric pen, stencil, sewing needle, iron, pliers
Trace the stencil
After cutting out the neoprene pieces, trace the stencil to them. Fuse tabs of conductive fabric to either end.
Sew with conductive thread
Thread a needle with conductive thread and stitch along the stencil pattern until you reach the tab of conductive fabric. Stitch the conductive thread to the conductive fabric with a few stitches to make good contact. Repeat for both sides.
Velostat
Layer the neoprene with the conductive traces inwards so that the stitches criss-cross. The Velostat goes in between.
Close
Sew the sensor together around the edges making sure not to sew too tight.
Test
To make sure your bend sensor is working. Connect either end to a multimeter and set to measure resistance (ohm). Your initial resistance should lie around 2K ohm and should sink to about 100 ohm when pressured by pushing down hard.
Attach
When attaching the sensor to the body one has to pay attention not to create too high initial pressure. Otherwise the sensor’s range is useless. We like to use metal poppers to connect the sensors to the rest of the wearable circuit.
Video: Neoprene Bend Sensor IMPROVED (Sheep demo)
Updates
Using Eeonyx stretch anti-static fabric instead of Velostat.
Trying out some new things. Stitching the conductive thread traces next to each other works fine in combination with Eeonyx fabrics, but not with Velostat. Conductive fabric traces work even better in this case.
YouTube Fabric Bend Sensor Playlist
Links
Patent for the Angular displacement sensor, patented by AEG in 1989, it is now open:
>> http://www.freepatentsonline.com/5086785.html
Wonderful tutorial from Images – Scientific Instruments on how to make your own bi-directional flex sensor:
>> http://www.imagesco.com/articles/flex/sensor-pg1.html
>> Images bi-directional flex sensor Instructable
Great tutorial from the Pulsar project on how to make bend sensors using Velostat:
>> http://www.pulsar.org/archive/int/timswork/Velostat.html
Summary of bend sensors on Sensorwiki:
>> http://www.sensorwiki.org/doku.php/sensors/flexion
Suppliers of manufactured bend sensors
>> http://www.imagesco.com/sensors/flex-sensor.html
>> http://www.flexpoint.com/
>> http://www.robotshop.ca/images-scientific-bi-directional-bend-sensor-flx-02-1.html
I can just see Glove Puppets playing an old game of Pong. As shown above vide moving the arms move the ping-pong ball.
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hi,
I want to use a modified version of this sensor (I need it in a different color and without the poppers). Would you want to share where you buy the neoprene with jersey bonded to it, or is that a ‘company secret’?
Are there alternatives to using the neoprene?
I tried a softer, foamed rubber, but it doesn’t work very well.
Thanks a lot in advance!
do you really think that we have “company secrets”?!?
you can find a range of neoprene distributors here:
>> http://www.kobakant.at/DIY/?p=457
if you are based in europe, then i would very much recommend sedo chemicals 1.5mm thick HS quality neoprene with polyester-jersey fused to either side!
Good stuff, thanks a lot!
which software of ubuntu will let me visualise the motion on screen
Hi, I’m having a problem with the sensor’s input slowly rising when pressure is applied. It happens even if I just set a weight on top of it.. the input won’t stay constant. Is that normal, or do you know what I may be doing wrong?
this is a great question and i’ve been meaning to test it. while there is some drift in the sensor that i would think comes from the materials settling, i don’t remember it being dramatic, and sometimes being amazingly stable. will hopefully run a test tonight and get back to you soon.
[…] that can be used in clothing. We used the concept of fabric bend sensors posted on the website of Kobakant.at. But the design of the bend sensors was something we had to discover ourselves, because the use of […]
[…] Bend Sensor blog post >> Instructable >> Flickr photo set >> Download Instruction […]
[…] Neoprene Bend Sensor by Kobakant How to Make Bi-Directional Flex Sensors by Scientific […]
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Hi! I having a problem with the sensor. When it is lay flat on the table, all of the LEDs light up. When bend, the results are the same. It seems like it doesn’t react to the sensor. The readings on the serial monitor are from 800-1000. Is there something that I did wrong? Please advise.
Thanks.
can you email a photo of your sensor? if possible also of inside construction. it sounds like the initial pressure on the sensor in it’s relaxed state is so high that the velostat is maxed out. or maybe the two contact sides of your sensor are touching directly.
Sure! May I have your email address?
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[…] Resistive carbon fused plastic Velostat Company: 3M Characteristics: Resistive material, good for making pressure or bend sensor with. Very cheap. example: Neoprene Bend Sensor http://www.kobakant.at/DIY/?p=20 […]