impact measurements (Charpy/Izod Impact Machine).

Hello, I was working on a simple Charpy Impact Machine that just uses a hammer and measures the difference in stat hight and end hight using a drag dial.

But I just thought, rather than using an analog dial and eyeballing the result, could I attach an and Accelerometers to the hammer and have it displace the peak hight on an LCD?

Never used and Accelerometers so thought I would ask here first before I go down the wrong path!

A simpler method may be to just have a rotary encoder on your pivot point and let the Arduino count pulses to determine how much angle of rotation was achieved and then convert to height

blh64:
A simpler method may be to just have a rotary encoder on your pivot point and let the Arduino count pulses to determine how much angle of rotation was achieved and then convert to height

oooooooh blh64 I like that Idea!!!!

EDIT TO ADD:

So much faith in your idea just ordered a 400 pulse optical rotary encoder.

And those ain't cheap! That is a lot of faith, appropriate given that this is a major religious holiday here.

ChrisTenone:
And those ain't cheap! That is a lot of faith, appropriate given that this is a major religious holiday here.

:smiley: Blessed be cheap products from Ali express, so not quite a sacrifice on the level of Good Friday/Easter!

Think the optical rotary encoder is going to be much simpler, but give more actuate results, and a little less daunting code wise....I struggle with the Blink code!!!

During my time as professional system designer and programmer the company wanted to sell an "Impact Detector". A "good hobbyist" had started the project, left the company giving me my employment. I never managed to create what the customers wanted.
They wanted to detect wheter the driver had cut a corner to sharp and bent the leg of the 40 feet high warehouse shelfs. They were not interested in detecting a crash into a wall.
We used an electronic G-force detector, later equipped with a top decting memory. We could detect a fatal crash into a wall but if the driver of the forklift truck released the pedal control by slipping it, the detector send an alarm.

I say, drop the idea unless You only want to detect things like how hard a driver uses the brakes or how fast a dragster accelerates at its best.

Railroader:
I say, drop the idea unless You only want to detect things like how hard a driver uses the brakes or how fast a dragster accelerates at its best.

Yeah, moved from the idea of using an Accelerometer using rotary encoder thanks to @blh64 as I really just need to measure 2 angles to get the needed data and work out how much impact was absorbed by the material, as in this use case they are set up to fail, small object, big hammer!

The Plan so far!

Try out Your idea. Such a mechanical system will filter out lots of vibrations that an accelerometer would pick up. I used the wrong Word in my previous answer. Accelerometer is correct, not G-force.....

I don't know what a forklift has to do with a Charpy impact tester, really. Other than that both have "impact" in the job description. You're not trying to detect an impact, but you're trying to measure how much energy it takes to break something. That's what an impact test does.

An accelerometer attached to the shaft can't work without affecting the measurement. The weight of the device and the wires are the problem. Then there's the problem of turning acceleration into displacement.

An encoder sounds like the appropriate sensor for this job, as it has a (nearly) zero turning resistance. Any significant resistance there means energy gets lost along the way and the measurement is affected, so that's anyway something that should be tested: do some swings with and without the encoder and see how high the hammer gets.

A serially built machine sold all ower the world in large numbers could never use a construction like this. Therefore an electronic, hightech accelerometer was used. That design was not fortunate. I brought the example up just to tell that impact detection might not be easy. Several MSC engineers failed to tune the design in.
This design migh have a chance to work.
As You say, a rotary encoder will affect the measuring. What about using a numer of photodiodes detecting the amplitude of the swing? I assume that Micro g-forces are not the target.

Issue is in order to get very accurate data, the encoder sweep would need to be larger than swing path of the pendulum.

As an example, your 400 count encoder is just going to be able to resolve a tad under 1degree rotation that’s if it can correctly count pulses at the speed max speed of the arc.

Now getting a high speed TOF sensor to measure the distance the hammer goes up on the upswing might be easier.

I have the feeling you don't know what a Charpy impact test is or what it measures.

You DON'T measure acceleration anywhere in this test. You don't even care about acceleration. An accelerometer is possibly the worst sensor for this test.

The standard test method: a hammer on a pendulum is raised to a specific height. The test sample, of specific dimensions, is at the bottom of the swing. The hammer falls, hits (and hopefully breaks) the sample, then continues the swing. What you're then looking for is how high the hammer ends up. The higher the swing, the lower the energy absorbed by the sample as it breaks.

So to digitise the instrument, what you need to know is how far it swings, and that's exactly what an encoder tells you. Come to think of it, this must be a quadrature encoder so you can tell when the hammer starts to fall back again, which is when the measurement is complete. It's only the part where it swings forward the first time after the test starts that you have to measure.

Another possible method would a distance sensor that measures how high the pendulum swings. A fast measuring time of flight sensor would be suitable. The main problem of this method is that if the pendulum swings only a little bit, it may not come in the field of vision of the sensor. A second sensor (looking horizontal) would take care of that. Being contactless, this method will not affect the measurement but is definitely harder to implement.

Slumpert:
As an example, your 400 count encoder is just going to be able to resolve a tad under 1degree rotation that’s if it can correctly count pulses at the speed max speed of the arc.

As long as you stay under a couple thousand pulses per second there should be no problem for the encoder, and no doubt there are high speed encoders that go way beyond that. Under a couple million a second will keep the Arduino happily counting all. I don't think that's a serious issue.

Railroader:
What about using a numer of photodiodes detecting the amplitude of the swing? I assume that Micro g-forces are not the target.

Yes, for this application I just need the be able to measure the force absorbed so planning on doing it like this

Slumpert:
Now getting a high speed TOF sensor to measure the distance the hammer goes up on the upswing might be easier.

I will have to look into that!

The maximum mechanical speed for the encoder is 1000 rev/minute so will be interesting to see how it does.

@wvmarle. Ok, a totaly different kind of impact situation. Still not the most simple task. Good luck!