How to use index pulse for homing purpose

[Zig]

I am in the process of building a machine, a simple xyz gantry.

The machine runs on EMC2 using linear scale / BLDC servo loops implemented in external hardware. EMC provides control signals step and direction and is configured a ssimple stepper motor controller.

Machine behaves quite nicely. It recognises end of travel limits. Test plots ( in lieu of actual machining ) comes up well.

The linear scale generates home index pulse.

I understand that EMC allows a motion control interface card to recognise the pulse.

Is there a way of interfacing the pulse NOT A LIMIT SWITCH to be recognised as home location in absence of such a motion control card.

Any suggestion is welcome.

[ger21]

This might work.

http://www.cncbuildingblocks.com/homeindex.html

[Zig]

Ger21,

Thanks for the info.

On further reflection I think all I need do is extend the pulse ( a monostable) so that EMC has time enough to reverse the direction of travel and cross the index pulse back fronm the other side for a second this time slower home latch pass.
( this is set up by making both home search and home latch velocities of same polarity / direction )
Will keep you posted.

EDITED 18.27 march 29 2008

Well a day has passed and the idea works. This would not work on a rotary encoder with many index pulses since multiple home positions would be available. I am using linear scales and since there is a unique index pulse it latches.


The solution could work with a rotary shaft encoder if one marked the range over which the homing is to take place and the range included only one index pulse. his might obviate the expense of home position switch and provide superior homing location provided by the index pulse.