What sensor can measure the change in the length of the elastic band?

Question

Do it yourself

Let's say there is an ordinary household elastic band, from 5 to 50 centimeters long and you want to measure the change in length when stretched by about 10%
. It is the usual elastic band that seems ideal, but systems of two thin flexible tubes moving one into the other are also considered.
The question is how can this be measured?

Answer 1

When the elastic is stretched by 10%, its length will change by 10%. Or is it other% you?
Don't want a laser rangefinder? - take ultrasonic or IR distance sensors.

Answer 2

Ruler =), two measurements, before and after.
Dynamometer - when stretching, a force arises, depending on the force, you can calculate the length knowing the initial (hello steelyard)
Either I misunderstood the question, or it was not formulated accurately enough.

Answer 3

Another option, which line with variable resistance, see slide resistors.

Answer 4

A load cell that attaches to the base of the end of the rubber band. It is difficult only with a good ADC for very good accuracy.
Strain gauges are in the form of strips of strain gauges that are glued to the metal, and then their resistance changes.
See about the bridge circuit of strain gauges.

Answer 5

I have not seen an industrial version, but the first thing that comes to mind is:
1. Does the rubber band change length? And what if you fix a wire on it in the form of an inductor, because when the distance between the turns changes, the inductance also changes.
2. Another option: fix two metal plates at some distance (for example), when the elastic band is stretched, the distance between the plates changes, and the capacitance of the improvised capacitor also changes.
3. You can also use a load cell (as suggested above), but this also has its own motives.
4. Pressure sensor? Well, it’s also possible, but there is one thing: it measures atmospheric pressure, so you have to shove it, for example, into a syringe with a sealed tip.

Answer 6

It would probably be possible to mold a bike out of something like a steering angle sensor or a rotation sensor connected to something like a tape measure. Well, or immediately take a laser rangefinder.

Answer 7

Smoke Hooke's law. But keep in mind that the proportional limit must not be exceeded.

Answer 8

Something like a Soviet curvimeter , screwed to the free end of an elastic band, won't it work?
The smallest collective farm possible, the design of the meter will consist of:
- a ruler with a hook, along which the odometer crawls
- the odometer
- a hook attached to the odometer.
A quick googling showed that a pointer curvimeter can be bought in tourist shops from 250 rubles.
For automation, instead of a curvimeter, you can screw the mouse upside down and read the wheel speed with any software suitable for this. Or, as an option, use the mouse itself as usual, mouse mileage counters are also available, it will not be difficult to correlate them with real centimeters.

Answer 9

Chinese electronic caliper.
It has a digital output with an accuracy of 0.005 (when filtering data).

Answer 10

Many thanks to everyone who is trying to help.
I realized that I couldn’t find a ready-made industrial one and I would have to do something of my own on my knee.
At the moment, it seems to me the most promising to take a magnetic rotation angle sensor for its small dimensions and ease of connection to the controller and, since the collective farm cannot be avoided, attach a spring-loaded coil with a rope to the shaft with a magnet for automatic return to zero position.
I doubt very much that something acceptable will turn out, especially considering the lack of love for needlework.
It is paradoxical that the necessary sensors, it turns out, exist in nature , but they are aimed at measuring large displacements with very small dimensions.
I want exactly the same but withmother-of-pearl buttons of small dimensions.
Thanks again to those who took part.

Answer 11

In order of delirium: you can try to measure the resistance of the gum itself.
You can attach a laser rangefinder and a reflector. Or the transmitter and receiver of the ultrasonic range finder are at different ends and take the distance out of the delay. In general, no one bothers to use a magnet and a hall sensor for example.

Answer 12

There is one idea, but you will not like it =)))
We attach a ferrite rod to the rubber band.
We wind the coil around the gum.
When the rod is moved into the coil, a significant change in its inductance occurs, which can already be monitored electronically. Well, for example, turn on the coil in a resonant circuit and put a frequency-voltage converter ...
The method is very accurate, there is no accumulation of errors, you can do it as miniature as you like, but you need to be friends with your hands, head and soldering iron.
Previously, pedals for electric guitars were made on this principle.

Answer 13

Dear community, I am writing what I dug up at the moment, suddenly someone is curious :)
1. Flexible stretch sensors (like what the doctor ordered) many thanks to podkovyrsty
http://robosensors.net/mechanical-sensors/flexible-stretch-sensors.html
http://www.imagesco.com/sensors/stretch-sensor.html
2. Miniature wire sensors (even miniature ones are very large, I didn’t find any smaller ones, but it’s a pity, it seemed to be exactly what you need and don’t need complex circuits, you can immediately or almost immediately connect to the digital part, depending on the sensor)
http://www.sensorlink.ru/pdf/01_SG5.pdf
http://www.sensor-systems.ru/product_13.html
3. Assemble the sensor yourself, here the rods inserted into the coils and attaching the coil to very compact magnetic angle sensors are in the lead.
http://www.prosoft.ru/products/brands/ams/362657/
Many thanks to everyone who took part!