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:
Unfortunately, the above device will not work if you want to generate
both static and dynamic forces - the output stage of the power amp is
capacitively coupled. Furthermore, the bandwidth is much wider than the
O.P. needs. If he is sampling at 200 Hz, then an upper frequency limit
of 100 Hz is more than enough, and 40-50 Hz is more realistic.
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.
The goal is to create a device that presses a fully weighted piano key
(even when it is moving) with the same force function as would a human
finger. This is a fairly significant force- a voice coil wouldn't be
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.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.