Re: Lowering Gecko Voltage

I agree op amps( with beefed output stages) would do better for
precise positioning with piezos, but now he's got to design the amp.

Also what piezo motor only needs +/- 10 volts. Is this going direct
to the 'crystal' or is there a drive involved that is contolled by
the +/-10v that you wish to produce from a Step.Dir controller.

Not an expert on piezo positioners, just tossing out ideas.
-Lee

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
>
> > Gary,
> > How about series resistors on either side of the piezo motor, and
> > maybe a R in parallel with the motor too. Say... run the Gecko at
> > ~30vdc and use 3 5ohm 10Watt in series, with the motor in
parallel
> > with the center 5ohm R. ( might need to play with the R values.)
> >
> > You need to find out if the motor is usable with a PWM drive,
> > otherwise you'll need to do some filtering to smooth the drive
pulses
> > to an averaging DC. Similar to what is done in a Class D
amplifier.
> >
> > This piezo electric linear motor has an encoder connected to
provide
> > feedback? Thats req'd.
>
> I really don't think this is a good way to do things at all.
>
> Piezo motors are high bandwidth capacitive loads. Electromagnetic
> motors are very low bandwidth inductive loads. The kinds of pulse
> width modulation approaches used to effeciently drive
electromagnetic
> motors are likely to fail horribly when applied to piezos - the
stack
> will try to wiggle at the PWM frame rate, and proportional control
of
> voltage will be nearly impossible, since the driver is only able to
> adjust the time average of current.
>
> This is really a job for op-amps. It is possible that you might be
> able to find a control signal inside a gecko drive which you could
use
> to run an op amp for driving the piezo... however that assumes
> that the gecko drive can keep up with your piezo stage, which it
> certainly could not do in the case of the small piezo elements I'm
use
> to working with.
>
> Chris Stratton
>
> -------------------------------------------------
> Christopher C. Stratton
> Engineer, Instrument Maker, and Horn Player
> ccs@m... 617 628 1062
> http://web.mit.edu/~stratton/www/brassbuild.html