Most of the machines I configure, I normally set them up to park close to the 
home switch, so that search times are relatively short.  And on the occasion 
that it isn't, it is usually no big deal to manually jog the machine close 
before beginning the homing sequence.  It is also why the homing sequence has 
two speeds.  With the right switch configuration, the machine should be able to 
search out the home switch at it's fastest speed, then use the latch velocity 
to precisely locate the home position (either using the switch or the index 
pulse of the encoder.) 

----- Original Message -----
From: "Chris Albertson" <albertson.ch...@gmail.com>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Sent: Wednesday, August 9, 2017 1:07:43 PM
Subject: Re: [Emc-users] Using laser time of flight sensor to home mill

One use I can think of for a low precision sensor is that you should be
able to home faster.   The motor can run at full speed until it gets close
then slow just before it hits a mechanical switch.   For this use case 10%
error is good enough.

On Wed, Aug 9, 2017 at 9:40 AM, Stuart Stevenson <stus...@gmail.com> wrote:

> Hi,
>
> Positioning the laser with magnets seems like an invitation to disaster.
> The laser WILL get bumped or jiggled out of position. Hopefully, the out of
> position would result in the machine not moving instead of moving to the
> wrong position.
>
> Using the laser to establish rough position (therefore eliminating  the
> need for a limit switch) to allow homing from the startup position seems
> "reasonable" if you can determine the laser position is repeatable enough
> to catch the encoder index mark on the correct rotation.
>
> To me, if you plan to home the machine, this sounds like a solution in
> search of a problem although I don't know the complexity of installing
> limit switches.
>
> thanks
> Stuart
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-- 

Chris Albertson
Redondo Beach, California
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