Stuff about sensors, a quick post.

Well, I’ve been looking around at torque sensors and found some interesting information. For one though, they are NOT cheap. Keep in mind that these are higher sensitivity sensors but it doesn’t seem to have an overwhelming bearing on the overall price. for example.

Optical, high sensitivity sensor, ~$6000
Magneto-elastic sensor, ~$2000
Strain gage based, ~$4300

While this is expected, it’s still quite a cost on a per-unit basis. interesting.

Another little tid-bit I picked up is this.
Magneto-Elastic sensor document

Anyways, I’ll keep looking for a cheaper unit, though, I doubt I’ll find one cheaper than the unit I developed. Perhaps I’ll machine a small enclosure with precision bearings and develop a more robust and practical design. I have some conductive graphite for the brushes in order to reduce noise and the brushes could be replaceable. Might try it.

Creating a strain gage coupling

So now I have to find some way of measuring the torque applied between the two shafts of the viscometer. Here’s my idea.

Strain Coupling Model View
Strain Coupling Model View

What you can’t see is that I plan to manufacture it out of plastic, that way the strain gage experiences the most out of the deflection of the part. I’ll use a flexible polyurethane bonding agent for the strain gages, allowing the forces of the strain to work without breaking the bond.

Here’s a through model view:

Strain Coupling Transparent View
Strain Coupling Transparent View

Of course, it only took me a few minute to make this model but it helped me see if what I was doing would work, I also used FEA to see if the forces would be transmitted where I wanted them. The FEA results were promising, nice even strain along the gage surfaces. (Those gauge surfaces are seen in light blue). You can see though that the hole through the side relieves some strain on the strain area, though, this shouldn’t be an issue.

Strain Coupling Strain Test view
Strain Coupling Strain Test view

Here’s an image of the stress as calculated by Cosmos

Strain Coupling Stress Test view
Strain Coupling Stress Test view

Well, hopefully this will work. First I need to get the strain gages to provide reliable results. By using two of them, temperature concerns should no longer be an issue and should help mitigate innacuracies. I’ll post pictures of the finished part, though I don’t think I’ll do it on the NC, I’ll just do it manually, it may look like ass 😉