Controlling a strobe to automatically capture rotational speed

[dacad]

This is pretty far out there but I figured, if I don't ask, I'll never know if somone has thought about it.

We use an LED strobe to measure rotational spped of a product during testing. Basically, the strobe pulse rate is adjusted until it matches the RPM's of the rotation and due to the effect, the rotation appears [relatively] stationary.

The particular strobe device I am using has some input/output control, for instance, I know I can read the rate on the output and I think I may be able to control the rate on the input.

Assuming I can control the rate, the big question is, are there any [somewhat simple] methods anyone knows of that would allow me to determine when the strobe rate matches the rotational speed of my product.  I would think it would require some type of camera setup that monitors the area of rotation and can automatically 'see' when the apparent rotation 'due to strobe effect' effectively stops.

Don't think I will have a lot of time on current project to implement this (unless it really IS simple) but am wanting to plan for next level and make sure I start feeding the seeds for buy-in down the road.

Any thoughts appreciated

Doug

[Don_Phillips]

That sounds entirely too complicated.  Strobing, calculating the difference via a camera, etc.  You would probably need to implement some kind of PID control to match speeds, etc.

If you have some flexibility you might consider a rotary encoder instead.  It is basically a round plate with holes mounted to the axis.  A light is positioned behind it and as it spins you can read the pulses (which directly gives you the speed with some basic math).

http://en.wikipedia.org/wiki/Rotary_encoder

[dacad]

Yea  I have used encoders on other projects but I don't have an option to physically mount anything to the product. Hmmm.  Perhaps I could have an encoder on a shaft that has an elastomer interface to engage the open end of the unit. Just have to be real careful about causing a change in speed from induced drag.

Like I said, pretty far out there.

Thanks

[Don_Phillips]

No mounting?  Hmm.  If the rotational part has "features" (I.E., grooves or parts that stick out) you might be able to use a reflective sensor.  Same idea as a rotary encoder but the light is directed to the part itself and as features pass by you can read the variations in light intensity.  Highly dependant on any features being present and material type.  I will continue to think about it...