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I am working on a project where I need to determine the density of a balsa wood strip.

I know the length and height of the strip. The two measures left to take are the weight and the thickness of the strip.

To achieve this, I am using an Arduino Uno. The weight measure must be accurate to 1 g; I achieved this with an HX711. In the thickness measurement I have problems, because it has to be accurate to 1 mm.

The strips are between 17 cm thick and 1 cm thick. I have tried using an IR sensor, ultrasonic sensor and laser sensor but all of them give me bad readings. This is because the environment where the machine has to work is in a balsa factory, where there is noise and dust.

How can I get this measurement as accurate as I need?

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    $\begingroup$ How do you know the length and width so precisely? $\endgroup$ – hazzey May 12 '15 at 0:56
  • $\begingroup$ Related:Distance sensors with accuracy of 1mm $\endgroup$ – Chris Mueller May 12 '15 at 1:16
  • $\begingroup$ Can the sensors look at the balsa strip from the side in your application? $\endgroup$ – Chris Mueller May 12 '15 at 1:19
  • $\begingroup$ Use a ruler? More seriously, measurements in noisy conditions can be very difficult to do with high accuracy. What sort of throughput do you need and how bad are the vibrations and dust. $\endgroup$ – nivag May 12 '15 at 8:39
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The thickness is pretty easy. I'd add a rotary encoder on a cam shape, push the cut balsa under the cam till you see max reading. You'll have to create a lookup table for angle vs observed height against a standard. Cam should return to zero via gravity (its a law!) but you can add a torsion spring if necessary. You will have to choose materials, finishes and thicknesses (weights) so as not to dent the balsa wood. Travel is from left --> right. Obviously you can NEVER back up the travel of the balsa wood in the sketch below. That will immediately cause a dent.

thickness gauge Dirty factory environment, the weight is much more difficult. What about a postage type of scale? something with an accurate strain gauge measuring system inside? I'm thinking a scale where the "table" is either a metal mesh or metal mesh with bearings so the balsa can ride over it. Mesh because its less likely to be affected by dirt and accumulated crud. Bearings if you need it. Obviously you will have to pick length that works, so automation doesn't adversly affect scale performance. Pick up item via 'fork' that doesn't interfere with scale table (motion for fork lifting device via planar 4 bar mechanism?)

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If the balsa can be measured by contact based methods you can use an arm and roller or roller and plunger or various other displacement based means.

If contact based means are not acceptable you should have said so.

There are many things missing from your description which MAY be relevant. As you do not know a good solution you also cannot know how relevant various aspects are and you should maximise what you tell people if you want good answers.

Full dimension range? mass range? rate of feed range? how handled? other ?

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