Re: controlling hydraulics with Mach 2 or Turbo CNC

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Todd W. Syssa"
<procisionengineering@y...> wrote:

>
> There are two solenoid valves in this proportional,
> directional valve. I have other valves but they are
> simply on/off.
>
> The hydraulic valve takes an input signal of 12V .6
> amps...this is where it just starts to flow fluid in
> one direction. Maximum flow (6GPM) is at 12V 1.2
> amps...any amperage in between will control flow with
> by a proportional amount (and it is pretty linear.)
>
> Simply give the same signal to the opposing valve and
> you start flowing fluid in the other direction,
> proportional to the current in the same manner.
>
> What I was thinking was to use Mach 2, get a rutex or
> gecko drive to control a servo motor from the step
> pulses from Mach 2...and now I will have varying
> voltage depending on which feedrate I use, which could
> be fed to a converter to vary amperage to the valves.
> The current could be shifted from one valve to the
> other by means of a relay board when Mach 2 tells the
> driver to go the other way. (for reversing directions)
> The system would have to be tuned down to avoid
> chatter. Is this idea full of smoke?
>
> The other way to do it is to build a counter (thanks)
> and card all from scratch...my dad would have to come
> in here though...lol
>
> Thanks for all the suggestions guys and gals.
> Not sure which way I will go yet on controlling them
> though...I would like to be able to have an off the
> shelf CNC package control the whole
> machine...so...this will be interesting.
>
> Luckily I have my dad who is an electronics guru
> (Allied Bendix Aerospace retiree).
>
> Todd W
>

If you boil this down to its basics you need an output voltage that
is porportional to a fluid flow. If you think about it you have
position information based on an encoder. The PWM output from the
computer (or motor control module will have to be "integrated" to
provide a DC control voltage that is porportional to the PWM
waveform. While this is easy to do with something like the LM2907
chip you have to throw in the fact that positional information needs
to be part of the feedback. This is a closed loop control (with a
really low frequency of operation). MACH2 does not in itself support
closed loop control and unless you do use an external closed loop
motor control (i.e. Gecko) you will have to use EMC and Jon's
approach. You still have the challenge of taking the PWM output and
making it control your setup. It seems a waste and redundant to use
a motor to control something that already has control built in. You
could of course run the output of the PWM motor control into an RC or
LC network to provide an output voltage. It would not be linear but
with the feedback you are going after a position rather than a linear
system.

You might want to look at the low cost servo controller IC from Rutex
and combine that with a 2907 to get a linear output voltage. Have
your Dad check out the chips at www.rutex.com. They will take step
and direction and give you PWM out based on the position of an
encoder. Feed that to an LM2907 circuit like th one in the files
section and you have a DC voltage output that is porportional to
position. You may have to buffer the DC to run your valve. MACH2
then can be your controller software if you so desire. This would
end up being a lower cost and simplier design.