RE: [CAD_CAM_EDM_DRO] EDM wire tensioning

A micro generating a PWM signal for your winder motor based on some input
would be easy (if you're a micro kind of electronics guy) it'd save you half
a bridge. Philips make some good power op amps, up to about 25W I think.
As for sensors. The homebrew options that spring to mind are:

A wedge shaped paddle that moves in front of an LDR, angle of wedge
determines rate of change of the value of the LDR.

Hall effect, something like a UGN3503 and a weak magnet on the tensioning
arm.

I'm told that there are some proxes that have a linear output..

All this is being on the assumption that you cant use a potentiometer as the
pivot for the tensioning arm?


Hope that helps

PK

> -----Original Message-----
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Graham Stabler
> Sent: Thursday, 6 April 2006 10:00 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] EDM wire tensioning
>
>
> I'm still making some progress on my micro wire-EDM, I now
> have 5000m of 0.05mm tungsten EDM wire and a small RC based
> sinker set up based on Ben Fleming's book but modified to use
> stepper motors and my ballscrew actuators.
>
> As a reality check I am going to try some single axis cutting
> putting the wire through a simple guide head to work as a
> chop saw in effect.
>
> The next stage is to work out the wire tensioning side of things.
>
> On the machine I have used the wire spool is held on a
> moterized spindle before passing around a roller with an
> electomagnetic clutch/break before going through the rest of
> the machine and to a motorized pinch roller that pulls the
> wire and determines the speed.
>
> However with 0.05mm wire I think I can probably get better
> tensions using gravity, I have done something a little like
> this before when winding coils in 0.02mm copper from a spool
> that did not allow the wire to be pulled from the end. I
> mounted the spool on a gear motor and then threaded the wire
> through an eye at the end of a hinged and weighted arm. The
> arm could trigger two reedswitches depending on whether it
> was pulled up or alowed to drop. The upper switch latched
> the wire spool motor on and the lower turned it off. It gave
> a bang bang control that was enough to make breakages
> uncommon as long as I wound at a speed slower than the wire
> spool motor.
>
> I want to do something like this again but I don't want it to
> be bang-bang as the tension will lower as the weight it
> lowered and increase as it is raised, at least during the
> acceleration phases.
>
> I guess a simple op-amp based feedback control to a bridge
> controlling the motor would seem sensible much as you would
> find in an RC servo.
> What should provide the feedback is what I need input on. I
> could use a LVDT but they are a little costly, alternatively
> a single turn "servo pot" perhaps, they are very easy to turn
> and a lot cheaper.
>
> Suggestions appreciated. I even wondered about an optical
> approach with an LED in a tube getting closer or further from
> a sensor.
>
> Graham
>
>
>
>
>
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