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Author Topic: losing steps  (Read 6715 times)

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Offline Hood

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Re: losing steps
« Reply #10 on: December 15, 2010, 07:45:25 PM »
Ok it is steppers but there seems to be some sort of closed loop similar to servos. Problem with steppers is if they are loosing steps its because they are stalling and have no more to give so they cant really be corrected and really the only thing that can be done is to stop them and fault the control. It may be possible to catch them just as they are starting to stall and try and rectify the problem but personally I cant see how that will work and it may actually be where your out of position is coming from. It will all depend how small/large the error allowance is in the loop.

Hood

Offline RICH

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Re: losing steps
« Reply #11 on: December 15, 2010, 08:47:30 PM »
So not knowing how the loop actualy works ,then the only thing one can do is adjust the machine to get it as good as possible, and then find the appropriate velocity and acceleration settings  that
provide for reliability.

It's tough to adjust to get "good as possible" unless you measure. If you have a torque indicator you can adjust the gibs, bearing preload, etc. and see the affect of the adjustments.
ie; tight may mean it takes say 60 in oz to rotate the screw as compared to loose which may mean 20 in oz required. Now when running fast and your at the upper end of the stepper speed
there is not much torque left , so say you only have 60 available and if tight, you have nothing left for machining, and the stepper is likely to skip no matter what control is used.

Just making the point that, without an adjusted machine , software settings or controls are not true to their intended use.

RICH
Re: losing steps
« Reply #12 on: December 17, 2010, 04:47:29 PM »
I'm still trying to absorb all of this and how to proceed. According to who I bought it from, it is not suppose to skip steps, it is suppose to stop. I don't know but it did. This has happened since I have been re-tighting things back up. So will try to back off a little. I don't know enough about "velocity and acceleration settings  " to change those. Thanks for the help. I appreciate all of your guys help.

Offline Hood

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Re: losing steps
« Reply #13 on: December 17, 2010, 05:15:45 PM »
The way I am seeing things is if the closed loop is sloppy it may take quite a bit of missed steps before the error is thrown. Is there a way to adjust the loop?

As for Accel and Vel they are in motor tuning, from Config menu. Lower the Vel and Accel settings by half and save axis and see if it helps. If it does then you can try increasing one at a time until it becomes a problem again then back off a bit.

Hood

Offline stirling

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Re: losing steps
« Reply #14 on: December 18, 2010, 06:27:15 AM »
Is there any way to completely disable the "advanced Digital Sync Lock Servo (DSLS) control technology."? because I'm thinking this might be causing your problems. Certainly your 0.06 inch out of pos is 480 steps out if my maths is correct - which if nothing else says your "advanced Digital Sync Lock Servo (DSLS) control technology" is as much use as a chocolate tea pot. BTW is this 480 steps missed or added? - because if it's added, then it's definitely the DSLS that's the problem.

Also (again) if my maths is correct then I make your "High power electronic chopper drive amplifier" (goodness - are these suppliers over egging their pudding or what?) half step drives - so I'm wondering if Sherline mode might be worth a try - but others will know more about this than me.

Cheers

Ian

Offline Hood

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Re: losing steps
« Reply #15 on: December 18, 2010, 07:23:03 AM »
Yes Sherline may work better, especially as pulse width of 9 helped before it would suggest the wider pulse is required. Just make sure your kernel is 25KHz if you try sherline, then again maybe selecting sherline automatically puts it  to 25KHz.

As for the DSLS  I am thinking it could be a couple of things,
First  its not tripping out because the loop is set so slack it is allowing position to be off by a lot before it trips. The reason it is getting out is due to the motor missing steps ,either due to tight axis or could even be the drive is not seeing the steps, due to pulse width being to low.

Second is like Ian says and its the drive putting out extras because it sees the motor not getting there but then its overshooting.

So definitely worth disabling it if possible as it will definitely help track down the issues.

Hood
Re: losing steps
« Reply #16 on: December 18, 2010, 02:21:27 PM »
Quote
BTW is this 480 steps missed or added? - because if it's added, then it's definitely the DSLS that's the problem
When I checed my zero in X, it showed minus .060 and shoud have showed zero.
I am going to try to cut the part today.

Offline stirling

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Re: losing steps
« Reply #17 on: December 19, 2010, 04:18:20 AM »
When I checed my zero in X, it showed minus .060 and shoud have showed zero.

OK but it's not just where you ARE (X-0.06), it depends on where you've COME from.
If you'd come from (say) X1 and commanded X0 and it's at X-0.06 then that would be 480 ADDED steps.
But
If you'd come from (say) X-1 and commanded X0 and it's at X-0.06 then that would be 480 LOST steps.

Offline RICH

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Re: losing steps
« Reply #18 on: December 19, 2010, 07:13:08 AM »
Are you loosing position on both axes or just the X?
Is it random and not repeatable......ie; may be happening at anytime while running the program?
Are you using backlash compensation?

Can you post the Gcode for the file your running?
RICH
Re: losing steps
« Reply #19 on: December 20, 2010, 09:59:56 AM »
It ran through "bottom.NC" first. Then I had to make make a modification that resulted in moving my starting z down .005. then I modified my drawing and repost the code as "bottom_redo hinge face.NC"
ran the this  code  and had the problem. The time interval between codes was just en ought time to change the tool. Now when It started, I didn't pay attention to where it was cutting because it was going to cut some air first, which would have been on the left side of the part, then it move over in x approx .500 and that it when I noticed that it was cutting the wrong spot.

This happened 1 time when it moved  in y approx -1.5 during a face cut, was recommend to un-install and re-install Mach. did that and a few days later this moved in x happened. I was trying to see what was wrong before I ruined another part. I'm hoping the problem was the gibbs were too tight.