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Author Topic: not backing off home switch  (Read 4058 times)

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Offline cr2

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not backing off home switch
« on: January 15, 2012, 10:39:56 AM »
I recently replaced the mechanical home switches on my X and Y axis with NC proximity sensors. I have them connected independently (not in series) to a C-10 breakout board. I left the original mechanical switch on the Z axis. The proximity switches work well except that the machine does NOT back off the switches after homing. The Z axis still backs off the switch as it did before. Can someone tell if this is ok, or did I do something wrong. I will provide more information as needed.
Thanks,
Charlie

Offline Hood

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Re: not backing off home switch
« Reply #1 on: January 15, 2012, 10:42:09 AM »
Could be that it is backing off but just you are not seeing it as the prox possibly changes state in a shorter distance than the switches did.
Do the LEDs at the side of each axis turn green?
Hood

Offline cr2

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Re: not backing off home switch
« Reply #2 on: January 15, 2012, 10:45:43 AM »
To the best of my memory, they do turn green. I'll double check when I go back out to the shop, but I do remember checking for that when I set it up. Thanks for the quick reply. Your suggestion makes sense. I guess I could put an indicator on it and watch the needle as it homes.
Re: not backing off home switch
« Reply #3 on: January 15, 2012, 11:15:32 AM »
Your machine enters emergency stop due to this situation, correct?
I had a similar issue. The problem was on the cnc4pc board, the IC that is connected to the inputs micros. It is as 74H*********xx, I do not remember exactly.

Offline cr2

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Re: not backing off home switch
« Reply #4 on: January 15, 2012, 11:35:55 AM »
No, everything is working perfectly fine. The only issue is that it isn’t backing off the switches. I’m in the shop now and the LEDs in Mach ARE coming on when the switches are activated. I put an indicator on the X axis and slowed homing down to 2% so I could watch it. It stops dead at home every time. No back off at all.
Re: not backing off home switch
« Reply #5 on: January 15, 2012, 11:39:33 AM »
Your home is not your limit switch also? They are independent (you have a home switch and a limit switch)?

Offline Hood

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Re: not backing off home switch
« Reply #6 on: January 15, 2012, 11:40:59 AM »
I would say its OK just the prox change state so quick that you dont see any back off.
LEDs turning green and no E-Stop support that.
You could try homing then jogging at the smallest step increment you can and see if you can move back slightly before you trigger the E-Stop. Another thing is you could home, jog away then do a verify and see what Mach says. I am assuming Verify still works with the parallel port, its been a long time since I used the PP.
Hood

Offline cr2

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Re: not backing off home switch
« Reply #7 on: January 15, 2012, 12:13:28 PM »
I’m going to show my ignorance here. There are no limit switches on this machine. What I’ve done is put one prox on each axis and then a steel ‘trigger’ that the prox senses at the home position. I also have another trigger at the other end of the axis and I intended to use both trigger positions as limit switches. But I don’t know how to set it up in Mach. If I travel too far on any axis it hits the end with a big crunch. Of course, I’d like to know how to set it up to avoid that. I don’t like using soft limits…have had problems with them.

Hood: I don’t know what you mean by ‘do a verify.’ Also, my E-stop never gets triggered unless I press the big red stop switch.
Re: not backing off home switch
« Reply #8 on: January 15, 2012, 12:32:58 PM »
But you have your home switch set up in the configuration?
And when you request homing the axis starts the procedure for homing? or i am missing something?

Offline Hood

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Re: not backing off home switch
« Reply #9 on: January 15, 2012, 12:44:08 PM »
Ah ok I preumed yo had the prox set also as Limit switches.
If you have the prox at the end of travel and can trip it from either end then you can use them also as limits, just enter the same port and pins for each axis limit as you have for home. If you can only trigger the prox from one end then you can set up that end Limit with it by entering the same numbers. If you dont have it at the end of the axis then you will have to fit other switches or alter the prox so it does trigger at the axis extents.

Verify is a button on I think MDI page, you can press it and it should move your axis to the home switches and will tell you if there is a difference between the position Mach thinks you are away from Home and the actual. As long as you have not lost steps and your switches are accurate it should say the difference is zero or very close to it.
As said it is a long long time since I used the parallel port so I dont know if it still works or not.
Hood