RE: [CAD_CAM_EDM_DRO] MORE on : Repeatability of Home switches......

Hi,

The way I do it on my TurboTaig board is to include the stepper phase with
the limit switch.

That is, if your stepper drive electronics provide a "Home" output you can
use this in conjunction with the limit switch. The Xylotex
(http://www.xylotex.com) boards based on the Allegro 3977 provide this. They
provide an output when the stepper is at phase zero.

You can combine this signal with the limit switch so that when the limit
switch is activated, the limit signal is not activated until the stepper
reaches phase zero. This makes the position more repeatable. If you are half
stepping, the stepper will move up to another 7 steps once the limit switch
is active.

An explanation of how this works can be found at
http://people.smartchat.net.au/~homann/downloads/Instructions-1_0.pdf

Cheers,

Peter Homann
mailto:Peter.Homann@...
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
http://www.adacel.com <http://www.adacel.com>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 665


-----Original Message-----
From: doug98105 [mailto:dougrasmussen@...]
Sent: Friday, 4 April 2003 12:58 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] MORE on : Repeatability of Home
switches......


Group,

I've only casually followed this thread, but have actual numbers for
switch repeatability been posted?

IMO, a homing switch is worthless unless it has a repeatability less
than the finest resolution of the machine. If the machine can
program to .0001" then what sense does it make to have a switch with
less resolution/repeatability? I'm curious if any of the common
off-the-shelf switches will be accurate enough.

Has anyone come up with a sure fire way to ACCURATELY home an open
loop stepper axis?

thanks,

Doug


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