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  #1  
Old Fri 25 December 2009, 21:37
javeria
Just call me: Irfan #33
 
Bangalore
India
Proper Homing

Hi All, I have proximity switches as my homing and limits on the mechmate , the problem I am facing is that every time there is a power loss and I need to rehome and restart the axes is off by atleast one millimeter and its always like that ,

how to identify the problem and what would be the probably solution for this?

RGDs
Irfan
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  #2  
Old Sat 26 December 2009, 00:10
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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Hi Irfan, as you know I don't have any limit / proxy switches on my machine, so I cannot help you there, but what I do is to take my machine manually to my desired 0,0,0 point. I then start my router and make a small mark on the work surface on this 0,0 point.
If anything goes wrong..like loosing steps or power outage, I then drive it manually back to this 0,0 point. I also use this as a reference point everytime I tell Mach3 to GOTO ZERO to go and change a bit. This way I can quickly check to see if the machine is still on 0,0.
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  #3  
Old Sat 26 December 2009, 00:59
KenC
Just call me: Ken
 
Klang
Malaysia
I recon there are more then one way to solve your problem.

If you have the budget, fixing encoders is theoritical solution...

Linking E-stop circuit to the BOB's E-stop In is another. If I understand correctly, if the E-stops are linked, the Motion control software will halt & will not loss the position.

I do face frequent momentary power failure at my place, about twice weekly, 5~10 seconds at a time. I am tinkering with an idea of a bank of SLA batteries parallel to the stepper motor power supply capacitor, similar topology as UPS & a cheap off the shelf UPS for the PC. The battery should last half an hour or so at worst hence enable my MM to live through the interruption & if it is a prolong black out, I'll have time to shut everything down properly or start an emergency generator if I have one.
I see 2 potential technical problems,
1)I need a intelligent control to recognize the charge state of the battery bank in order to prolong battery life & avoid an explosion..
2) I need to ensure they are the same voltage with the stepper motor PSU.
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  #4  
Old Sat 26 December 2009, 02:29
javeria
Just call me: Irfan #33
 
Bangalore
India
Kobus - this case the point of reference is already machined

Ken its totally different, the reference offset stored in Mach is related to its homing position, once there is is a power loss ( 2 to 5 times daily ) the computer running the machine goes in estop / limit switch stop mode ( the estop is not linked to the BoB) but the limit switches are - this computer itself has a 10 min bkup UPS, which lets me store the offset values, when power is back again, all I have to do is to re home and tell Mach " Go To Z" and it goes to the previously set zero position.

experts pls help.
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  #5  
Old Sat 26 December 2009, 02:52
KenC
Just call me: Ken
 
Klang
Malaysia
Hi Irfan,
You already have a backup power for the stepper motors? Or else the machine should die instantly or until the capacitor dries up...
That 1 mm could be the micro stepping error... The software won't know where it stopped exactly... I think... & each step is 1mm?
Why not just try linking the E-stop to BOB? Isn't this suppose to tackle such situation?
How long is the normal duration of blackout? maybe a UPS like I describe could help?
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  #6  
Old Sat 26 December 2009, 04:14
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Irfan,

This is what I do. When you set up the 0,0,0 point for what you are going to cut, it is usually a little off from the piece you are cutting out. With an end mill in your router / spindle, or even a engraving bit, move down in the Z direction with the router / spinder turned on. This is your 0,0 reference point. If your power dies, you still home the machine but then you move to the reference point, place the bit into the hole, zero out X and Y. Move to another location to zero out the Z.

I personally don't think you need to have a battery backup system, when a simple reference point will work. Simple is always better.
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  #7  
Old Sat 26 December 2009, 08:08
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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Maybe Nils explained it better than I did. His method is exactly what I do....ride it manually to the hole...you get a hole in one
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  #8  
Old Sat 26 December 2009, 10:10
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Quote:
Originally Posted by KenC View Post
I am tinkering with an idea of a bank of SLA batteries parallel to the stepper motor power supply capacitor, similar topology as UPS & a cheap off the shelf UPS for the PC.
Ken my advice would be to just use an UPS. A UPS will do the switching work for you when there is no power, and will make sure the battery is always properly charged.

Some UPS systems do also have a output witch you can connect to 'something' (be creative here), but a normal 110V/220V relays will also work. You can then output this on a input pin on the BoB. When there is no power, you can instruct mach3/EMC2 to move the spindle up and old all processing of the piece. When power is back you can simply continue work on the exact spot you left off.

Would that work you think?

Ries
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  #9  
Old Sat 26 December 2009, 10:17
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Irfan,

You could also safe the initial 0,0,0 as an Active Work Offset under Offsets. I have not tried this but I am going to try it. Besure to save it off but when the power fails, you would home and reload the Active Work Offset and you are back.

I decided to test this idea so I went outside to the garage and it works fine.

Last edited by sailfl; Sat 26 December 2009 at 10:33..
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  #10  
Old Sat 26 December 2009, 13:49
mikefoged
Just call me: Mike #27
 
Randers
Denmark
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Hi Ifran

I think it is your speed..

I had the same problem with my zero, always a little bit off set.
Then I slowed down the Ref all to 20% and it is spot on every time now.
What speed is your ref all home set to?
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  #11  
Old Sun 27 December 2009, 01:07
KenC
Just call me: Ken
 
Klang
Malaysia
Ries,
I like you simplistic solution, will try it out when I'm ready. Thasnks
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  #12  
Old Sun 27 December 2009, 05:46
javeria
Just call me: Irfan #33
 
Bangalore
India
Mike I think your's is the right solution - I will chk that once I am at the workshop today, I have so much of the prototyping work lined up.
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  #13  
Old Sun 27 December 2009, 10:22
DMS
Just call me: Sharma #9 India
 
Rajasthan
India
Irfan,

I also use same method as Nils and Kobus, note down line # or find out which segment was being cut in mach .While restarting run from few lines back.
I also run Z zero routine.
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  #14  
Old Sun 27 December 2009, 10:40
javeria
Just call me: Irfan #33
 
Bangalore
India
I am inclined to use the limits bcos they are just so easy to use

I am getting good results after I have set slower speeds for homing - will investigate more on this - more tomorrow,
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  #15  
Old Mon 04 January 2010, 22:09
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
...did the slower speeds help? I found that the slower the home speed, the better re-home and useability. Even if I e-stop the machine, I have been able to re-run the file and go back to the part I stopped on. Not always, but close.
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  #16  
Old Thu 07 January 2010, 02:49
javeria
Just call me: Irfan #33
 
Bangalore
India
no sean they did not - i got it down to 20%, even then the same issue - off by 1.5mm on each axis!!!!

i am lost and don't know how to solve this out.
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  #17  
Old Mon 11 January 2010, 23:17
javeria
Just call me: Irfan #33
 
Bangalore
India
any one any more help ?
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  #18  
Old Tue 12 January 2010, 11:01
Polder48
Just call me: polder
 
Edam
Netherlands
Irfan

Although still in lurking phase and planning the build, is this treath maybe of any help for your problem?

http://www.mechmate.com/forums/showthread.php?t=1019

Just trying to help - Polder
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  #19  
Old Tue 12 January 2010, 11:51
javeria
Just call me: Irfan #33
 
Bangalore
India
No polder that thread does not talk about proximity switches at all
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  #20  
Old Sun 17 January 2010, 04:07
sprayhead
Just call me: Francis
 
sydney
Australia
Irfan, are your switches good quality?

Have you tried to use a different switch?
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  #21  
Old Sun 17 January 2010, 07:17
javeria
Just call me: Irfan #33
 
Bangalore
India
Francis I have to try that
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  #22  
Old Fri 22 January 2010, 12:47
javeria
Just call me: Irfan #33
 
Bangalore
India
seems that the x axis proximity sensor was faulty - got that fixed and its working much better
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  #23  
Old Sat 23 January 2010, 09:34
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Irfan,

I have a question, if you have your proximity switches set up, how did Mach allow you to operate with a faulty sensor. If one of my sensors is not reading correctly, I can not do any thing until I fix it.
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  #24  
Old Sat 23 January 2010, 23:41
KenC
Just call me: Ken
 
Klang
Malaysia
Maybe the switch is in that half-death situation, it works but not very well...
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  #25  
Old Sun 24 January 2010, 04:43
javeria
Just call me: Irfan #33
 
Bangalore
India
Nils - the sensor's nut got loose and i had not noticed that - it was 4mm sensing sensor and it had travelled down and started sensing metal always - this made the y car almost come down to earth- but the z assy held it in place.

the fault was due to it being loose.

btw did you get the files i emailed you - can you send me the horse again?

RGDS
Irfan
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  #26  
Old Sun 24 January 2010, 06:28
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Irfan,

My sensors have come loose also and things stopped running. The first time it happens you don't know what is wrong but now when things don't work, I check the sensors first.

I will email you.
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