Hi. I am trying to find the best way to use some data from a pressure sensor (force vs. time at 200 samples/s for a few seconds to be precise...) and reproduce the same force function (maybe with a solenoid ) at a later time with decent accuracy. Would some sort of sensor feedback loop work? Is this even possible? Thanks.
Sure it would. Closed loop control with almost any sort of pressure generator should work. You could use PWM on a solenoid, or maybe a dc motor on a compressor pump, etc.
The devil's in the details, but as a basic concept, a record, playback system seems quite resonable.
Might be kind of a fun project to do. Got any more details?
200Hz? You're going to need a voice coil positioner, as from a subwoofer. Here's a homebrew version with an accelerometer for feedback. Since you want to reproduce force, rather than position, this might be appropriate. This cost about $330 to build.
It appears to have moved to here:
For such low frequencies, you may be able to avoid the use of an accelerometer by closing the feedback loop upstream of the voice coil (i.e. no mechanical feedback, just electrical). To do this you'll need to calibrate the voice coil first by applying various DC voltages and measuring the resulting force and displacement functions.
One note of encouragement: I did this once to simulate the effect of a bird pecking on an object. It worked well, and the resulting force was impressive, but my setup was entirely open-loop - I just applied whatever voltage was needed to get the job done.
One last thing: remove the speaker cone with an X-acto knife, carefully preserving the voice coil suspension and the braided wires that connect to it. I also carefully sawed away most of the metal frame. I attached my mechanism to the remaining voice coil with epoxy glue.
-- Joe Legris
Not one from a small speaker, for sure. I have a voice coil actuator from an old HP "washing machine" disk drive here - 3" diameter, 4" throw, perhaps 1KW power handling, that can throw ans position a circa 300g mass through the full range and stop in 10ms. That's do it! But a lot of work/money to adapt.
Wrt measuring and reproducing the motion, you might be better off measuring the acceleration profile using a MEMS or piezo accelerometer rather than trying to reproduce the force function.
Ah. There's a neat solution to that problem. See U.S. patent application #20050211049. It's basically a solenoid-driven piano actuator, but with dynamic control of the current to get the desired force and position. You have to characterize the dynamics of a piano action for this to work, but that's not too hard, and you can generally assume that all the keys work the same.
John Nagle
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