Re: Perfect Homing Accuracy

--- In CAD_CAM_EDM_DRO@yahoogroups.com, cnc002@... wrote:

>
>
> In a message dated 10/24/2006 5:09:52 P.M. Eastern Daylight Time,
> salhab@... writes:
>
> Randy,
>
> I'am retrofiting an old cnc mill (Schaffner Swiss Made ) , I'am
> cutting Steel , Aluminum ... making Blow molds , I have to make it
> very accurate since I may not finish all the machining passes in one
> day and I have to home accuartly so as I can finish the rest of the
> machining the next day.
>
> Shadi Salhab
>
>
>
> I see, I take it then that the actual machining is not necessarily

going to

> need the same accuracy of 0.01mm you just want to make sure you go

back to the

> same point from which you stopped as closely as possible. I think

using

> either a mechanical limit switch or even a proximity sensor along

with the zero

> pulse on a good quality encoder will do the trick.

This will work only, if you stop the machine at the homing point,
ie. make the homing procedure before switching off the power.
The machine always start with both of the motor windings powered.
If you power down the machine, if it´s stay in a stepping where the
windings not are full powered, you always will have automatically a
offset.
You can test it, without changing somethings, if you power down the
machine after having homed the position, and then power it up, you
don´t have a offset.

Otherwise, capacitive sensors should be very precise and relative cheap.
I personally i don´t have used it.
Instead i have used encapsulated reed relays and magnets with great
success for repeatable homing and limit switch. This are of magnitude
cheaper. This includes the vane sensors based on magnets and
semiconductor hall effect sensors.

>
> Randy
>
>
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>