How can I accurately measure force using a pressure sensor?

[Kasper86]

Hi guys
I hope you can help me a bit to understand a problem.

I want to build a prototype of an insole/shoe which can meassure the force applied through a step.

I´m thinking of placing a small rubber tube into the shoe, and then bending it smoothly a lot of times, so it will cover most of the insole.
Then I would hook it up with a pressure gauge like this: http://dk.rs-online.com/web/p/tryksensorer/7191055/ , and use Arduino to send my readings to Matlab.

But I´m not sure I understand how the pressure will be in the tube. I guess the pressure will be equal on every small area of the tube and therefore also the same at the meassuring point of the gauge?
Lets say that the inner diameter of the tube is 0.5inch^2, and the total force on the tube is 500N.
These pressure gauges have a limit around 50-100kPa, and my question is then, how would you calculate the pressure affecting the gauge - so I just don't buy the parts and ruin them.

If there is anything I´m missing, please let me know :)

Best regards - Kasper

 

[Mech_Engineer]

Calculating pressure from the geometry you've described would be difficult, because rubber expands with pressure as well. Your pressure vs. force curve would be a nonlinear curve and dependent on geometry and material properties of the tube. You may be better off designing a piston in the shoe which compresses; or alternatively you might be able to use a mechanical spring and measure its dimensional compression.

 

[Travis_King]

This may help you:
Evaluation of Piezoelectric Film Sensors
for In-Shoe Pressure Measurement

 

[Kasper86]

Thank your for your replies. I had not thougt of the rubber exspansion :(
I´ll will look into the article you have mentioned. Thank you :)