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loosing steps
« on: March 18, 2023, 07:49:02 PM »
what would make a machine loose steps
using mach 3 with cnc4pc c62 break out board and teknic cpm-sdsk-2310S-RLN motors
set up machine and all was good for about 3 months.
then one morning the first cutout the ending cut did not line up with where it started
first thought motor was going bad swapped out for new motor ran motor setup per teknic
still off swapped new controll wires still no good
the longer the g-code file the more it is off
this is only happening on the X axis Y axis is good
did the axis calibration per mach
anybody have any ideas what to check next
thanks in advance
KE8MIR
Re: loosing steps
« Reply #1 on: March 18, 2023, 09:50:14 PM »
  You might try to go into motor tuning and reduce the acceleration/deceleration parameters but I don't think that is your problem.  Check for a mechanical bind which can be caused by lack of lubrication, bearing failure or contamination.  Barring that, I am not sure what your issue could be but I don't believe it is a Mach problem.

Ed
Re: loosing steps
« Reply #2 on: March 19, 2023, 03:03:56 PM »
Is there a way tell if the motor is pulling full load?
this is on a plasma cutter it should  have on load on the motor other than the  x axis rail
this machine is only 3 months old
Re: loosing steps
« Reply #3 on: March 19, 2023, 03:35:11 PM »
  Unfortunately I don't know of any way to monitor the motor load with Mach or any other stepper driver/control set up.  But that doesn't mean one doesn't exist, I am just not aware if there is.  AC and DC servo setups often, but not always, have the ability to monitor servo motor loads.  I would take the X axis motor off and try to turn the lead screw/ball screw by hand to feel for any drag, roughness or bind along the entire travel window. Is the lead screw and axis guides or linear ways protected from the environment?  If not, regular cleaning and lubrication is in order.  With that said, being 3 months old does not mean that you don't have an issue that might still be under warranty.

Ed
Re: loosing steps
« Reply #4 on: March 19, 2023, 03:47:02 PM »
Hi,
Clearpath servos can monitor servo load but relies on PWM of the HLFB output of the servo. Enquire of Teknics......the trick then is to have Mach interpret that
signal.

Other servos have separate channel for analog output and its just a matter of hooking a voltmeter to that output to monitor servo loads, but not so Clearpath.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: loosing steps
« Reply #5 on: March 19, 2023, 04:26:25 PM »
  Ah, I didn't realize his motors are servos.  My question then is why doesn't the system shut down for a following error?  Where is the encoder signal going?  I have an integrated stepper servo set up and the encoders report to the stepper drivers.  When there is a following error the offending axis drive shuts down and sends a fault signal to my control board setup.  Mach does not enter into the picture at all and has no concept as to why the fault occurred; it only knows that the C94/UC300ETH control setup is not happy.
  However, this does not answer why the axis is loosing steps.

Ed
Re: loosing steps
« Reply #6 on: March 19, 2023, 04:37:11 PM »
Hi,
Clearpath servos have one digital output, and its programmable. The most common use is that it be a combined 'Servo Fault' indicator that would combine various overload conditions
and Following Error. Has OP bothered to program the HLFB? Has he bothered to wire it back to the breakout board? Has he botherd to program the motion controller to
respond to a HLFB signalled fault?

Clearpath encoders are built-in and go direct to the control electronics in the servo.....they do not ever get presented to the outside world, including Mach4.

Quote
However, this does not answer why the axis is loosing steps.

There are a number of possibilities including electrical noise. Noise could potentially be in effect signalling extra step are required, so Mach issues 1000 Steps but electrical noise adds an additional 10.
Another possibility is that the servos are being overloaded or more likely being demanded of greater accelerations and/or velocities than its capability. That would be commonly detected as a
Following Error, but then maybe OP has not programmed it so.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: loosing steps
« Reply #7 on: March 19, 2023, 04:53:49 PM »
  It just occurred to me that the system may not be loosing steps but rather the positioning error is happening as the result of a loose coupling on the ball screw.  Is the motor direct coupled to the lead screw or is there a pulley involved that might be slipping?  If the system was working for three months without issues, what changed?
  All good points Craig.  I would think that electrical noise interference is an equal opportunity problem that would affect all axis' but with that said, are the encoder wires shielded and grounded appropriately? 

Ed
Re: loosing steps
« Reply #8 on: March 19, 2023, 05:24:40 PM »
wow that is a lot of info we ran a spare cable from the bob to the motor
there was no change in operations still loosing steps
this machine has a rack and pinion drive system on the x axis
and has four bearings that ride on a angle iron and are not protected from the machine
i am thinking that a bearing going bad
it is unfortunate that the builder of the machine went bankrupt the day after christmas
i am going to pull the bearings off tomorrow and see if the local supply house can track down
replacements will report back
thanks for all the feedback
Re: loosing steps
« Reply #9 on: March 19, 2023, 05:31:22 PM »
Hi,
I don't think that is the right move. I think just throwing parts at the machine without trying to find a cause is a good way to waste
time and money.

If the machine is loosing steps then it should fault out 'Following Error'.

Do you have the HLFB programmed to signal Following Error? Do you have your motion control board ready to accept and act on a Following Error?
If the machine is loosing steps Mach should know about it.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'