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Author Topic: Improved Home Switching Idea?  (Read 1474 times)

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Improved Home Switching Idea?
« on: April 03, 2016, 05:36:01 AM »
If we assume a machine with all limit switches on one input and a separate input for each home switch and wire it up with any old decent Normally Closed micro-switch at end of travel we get home positions but with accuracy and repeatability which is often dismissed by owners of pro systems and rarely proves good enough to pick up halfway through a finishing operation.

But what if we add a cam somewhere on each stepper shaft or ball-screw which operates a second switch wired in parallel to the end of travel limit switch for that axis?
The cam switch will operate once per turn but the home circuit will only open with both switches open, tune the cam switch to open/close a fraction of a turn after the linearly actuated switch is open and the accuracy and repeatability should be significantly better than is achievable with just linear switching.

Sound feasible?

 - Nick

Offline Tweakie.CNC

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Re: Improved Home Switching Idea?
« Reply #1 on: April 03, 2016, 06:43:25 AM »
You may have just re-invented the wheel but so what I think that is a brilliant suggestion.

(I have just made a minor repair to my mechanical jukebox and that has exactly the system you describe only it uses an optical switch & slotted disc on the stepper).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Improved Home Switching Idea?
« Reply #2 on: April 03, 2016, 06:50:00 AM »
Thanks Tweakie!
I know the concept of a shaft encoder is old but the idea was a way to massively improve homing accuracy and repeatability in a way that would be accessible to everyone who's already added or is considering adding homing switches to their machine ;-)
Re: Improved Home Switching Idea?
« Reply #3 on: April 03, 2016, 08:51:20 AM »
If we assume a machine with all limit switches on one input and a separate input for each home switch and wire it up with any old decent Normally Closed micro-switch at end of travel we get home positions but with accuracy and repeatability which is often dismissed by owners of pro systems and rarely proves good enough to pick up halfway through a finishing operation.

But what if we add a cam somewhere on each stepper shaft or ball-screw which operates a second switch wired in parallel to the end of travel limit switch for that axis?
The cam switch will operate once per turn but the home circuit will only open with both switches open, tune the cam switch to open/close a fraction of a turn after the linearly actuated switch is open and the accuracy and repeatability should be significantly better than is achievable with just linear switching.

Sound feasible?

 - Nick
My lathe has no limit switches (silly me) but I use a standard microswitch in conjunction with an opto sensor on a slotted disc on the other end of the double shaft stepper on the X-axis. The microswitch is wired in series with the opto signal output that feeds into the BOB. It is adjusted so that the N.O. switch closes just before the axis reaches zero & the next "on" opto signal then gets through to the BOB/Mach.  It homes VERY accurately & repeatably.  Cobbled it up for a trial back in 2012 & been loving it ever since.
« Last Edit: April 03, 2016, 08:53:35 AM by DICKEYBIRD »
Milton from Tennessee ya'll.
Re: Improved Home Switching Idea?
« Reply #4 on: April 03, 2016, 08:51:57 AM »
Sorry, double post
Milton from Tennessee ya'll.