Re: [CAD_CAM_EDM_DRO] hydralic bed control

How complicated could these valves be?

You'd need one for each direction of travel (i.e. X+ and X-), but a more
creative person could probably combine the functions into one unit.

A double o-ringed piston moving in a honed cylinder with an input port on
the closed end. The ouput oriices are drilled in line, the more holes you
expose, the quicker the bed moves. The piston could be controlled by a
Stepper motor driving a screw.

There would also need to be a Spring loaded bypass port to prevent
over-pressure when the cylinder was closed. (These are available
comercially, Grainger)

The two units would be Mechanically or software interlocked to prevent both
ports (X+ and X-) open simultaneously.

----Original Message Follows----
From: dave engvall <dengvall@...>
Reply-To: CAD_CAM_EDM_DRO@egroups.com
To: CAD_CAM_EDM_DRO@egroups.com
Subject: Re: [CAD_CAM_EDM_DRO] hydralic bed control
Date: Sat, 29 Jul 2000 08:51:55 -0700

Ejay Hire wrote:

> Disclaimer: I haven't done specifically what you ask about, and I don't
> know how much backlash is present in a hydraulic system.
>
> If I were going to attempt this, and not a lot of people had said it
> wouldn't work, here is what I'd do.
>
> 1. No power steering pump. Hydraulic pumps are less than $100 and will
> last longer, run cooler, and provide more stable volume.
> Get them from Grainger or Princess Auto(The catalog, not the web store)
>
> 2. Linear encoders provide feedback to the Controller. This will have

to

> be a closed-loop system
>
> 3. Electrically controlled variable rate hydraulic valves.
>
> With the proper controls, it wouldn't seem to be very different from a

servo

> system.
>
> ----Original Message Follows----
> From: dave engvall <dengvall@...>
> Reply-To: CAD_CAM_EDM_DRO@egroups.com
> To: CAD <CAD_CAM_EDM_DRO@egroups.com>
> Subject: [CAD_CAM_EDM_DRO] hydralic bed control
> Date: Sat, 29 Jul 2000 07:38:06 -0700
>
> Hi,
> I have an old horizontal mill with a hydralic bed. Has anyone tried
> control of anything hydralic using a automotive power steering unit?
>
> Dave

Hi again,
Back in the dark reaches of my memory is the recollection that the first
cnc's were hydralic and while they may not have been a
good as the electircal stuff they worked. I've spent some time talkng with
one of the electronics people at Dowty Aerospace that
does a lot of test stuff and he assures me good hydralic servo valves are
spendy.....really spendy....which is why I'm considering
using a power steering control unit.
The other option might be a series of solenoid valves with binary weighting.
i.e. hydralic D/A. :-)

Dave

>
>

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