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axis zero moved
« on: June 17, 2013, 08:55:00 AM »
I am still working bugs out of the system but I can't see why this happened.  It's a simple mill conversion.  Twice running one set of code my y0 moved by about .500", consistantly to the same spot each time.  The other 10 times or so I ran the program it stayed put.  I figured it was a glitch I forgot about it.  Yesterday it happened again in a different program.  I simple drill counterbore of 2 holes.  It just never moved to the second location and when I stopped everything and hit go to zero I was off by exactly distance between the holes.  So exact I put it in set mode and  jogged over that amount and rezeroed the y axis and reran the program and it worked fine and did so for the remaining 3 parts.  Where should I start looking to prevent this from happening again.  I am also still using demo mode, it this something with that?  I need to register it anyway, just wanted to get it all working first.  But no reason I can't buy the license now.
Thanks,
Don
« Last Edit: June 17, 2013, 08:59:31 AM by DonMarkey »

Offline Hood

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Re: axis zero moved
« Reply #1 on: June 17, 2013, 01:36:23 PM »
If steppers could your axis be stalling? Can you hear noise when it happens?
Hood
Re: axis zero moved
« Reply #2 on: June 17, 2013, 03:11:27 PM »
I might have two issues.  Earlier today I was running it with the spindle off so it was real quiet. I hit go to zero and the dros moved on the x+y but no movement or sound, the z worked fine.  I jogged around fine and hit go to zero again and they all worked but the x and y went to the wrong location.  I few minutes ago I hit go to zero and you could hear the x stall, but it jogged fine.  Yes steppers and no I never really tuned them right, I just got them moving without sounding bad and got the steps per accurate.   I need to read up I don't really have a clue on tuning these things.  The drivers are adjustable as to the number of pulses per step and I just set them for 2000 kind of as a guess.  Problem is it is a manual machine conversion and I need to keep it running as it is my only machine so I don't have much down time.  IS there a good tutorial on tuning steppers? 
Thanks,
Don
« Last Edit: June 17, 2013, 03:13:02 PM by DonMarkey »

Offline RICH

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Re: axis zero moved
« Reply #3 on: June 17, 2013, 10:20:43 PM »
Start by having the velocity set to a low number, say 10 ipm and the accel = 1.
Now just keep doubling the the vel until they skip. Say they skip at 120 ipm, then somewhere between
60 and 120 is the max velocity. So try 100, if they don't skip then leave it at that setting. Now at 100 increase the accel to 2 and start doubling it until they skip. Say it skips at accel =6, then reduce the vel to say 80 and try.
You will find a max velocity and accel value quite quickly.

Whatever that value is that they skip at some max vel and accel reduce the velocity by maybe 30%. Now you
do some testing while machining and over time you will have a reliable value for vel and accel.

Just trial and error. Even if the values are calculated you still need to test and confirm.
Of course having a motor curve always helps.

What you really want is power and that is speed x torque.

If you can set the drives for microstepping and greater than 10 is of no value.

BTW, make sure the steps per unit are correct.

RICH
Re: axis zero moved
« Reply #4 on: June 19, 2013, 08:02:29 AM »
Thanks Rich, I will play around with it.  I was reading on another post about the same issue and someone commented on the step pulse polality.  How do you know if it should be set to active low or high.  These are the drivers I have http://www.wantmotor.com/ProductsView.asp?id=271&pid=82
Don
Re: axis zero moved
« Reply #5 on: June 19, 2013, 08:25:09 AM »
Won't let me edit for some reason.  Sorry this is the driver I have.  Probably the same though. http://www.longs-motor.com/productinfo/detail_12_80_137.html
Don

Offline stirling

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Re: axis zero moved
« Reply #6 on: June 20, 2013, 05:07:55 AM »
I was reading on another post about the same issue and someone commented on the step pulse polality.  How do you know if it should be set to active low or high.

If your datasheet doesn't tell you, you can find out like this...

Those drives can be wired to allow your port pins to either source or sink current. i.e. you have individual access to both the anodes and cathodes of the opto-couplers (PUL+/PUL-).

Ideally you should have your 5Vdc supply on PUL+ and your step signal on PUL- (sink mode). If so then...

Disconnect your step wire from PUL- and connect a short wire.

Touch it to ground and then remove it. Did it step when you touched it or when you released it?

If the former then you set Mach active low. If it stepped when you released it then set Mach active high.

-----------------------------------

If on the other hand you have PUL+ connected to your step pin and PUL- connected to ground (source mode - not ideal) then...

Disconnect your step wire from PUL+ and connect a short wire.

Touch it to 5V and then remove it. Did it step when you touched it or when you released it?

If the former then you set Mach active high. If it stepped when you released it then set Mach active low.

Note: with microstepping set you may not be able to detect a single step (try touching the motor and feel for it). Alternatively you could set them to full step just to perform the above and set them back when you're done.

Ian
Re: axis zero moved
« Reply #7 on: June 20, 2013, 09:20:17 PM »
Why is it more ideal to wire it to sink instead of source?  I am pretty sure I wired it to source, easy enough to change it around but what is the advantage?
Thanks,
Don

Offline stirling

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Re: axis zero moved
« Reply #8 on: June 21, 2013, 04:35:40 AM »
Simply because most TTL outputs can sink more current than they can source. Therefore you're less likely to pull down the voltage. Therefore your system is more likely to be reliable.

Ian