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Author Topic: Am I loosing Steps, and what should I do  (Read 13981 times)

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Re: Am I loosing Steps, and what should I do
« Reply #30 on: July 22, 2016, 03:00:29 PM »
Gas springs are usually a fixed beginning force rating.  You must apply that amount of force to move it off the stop, then it increases about 10% over the full stroke.  Because it uses a fluid it also acts as a damper keeping quick motions from happening as well.  Some are adjustable, they come fully pressurized, but a bleed screw lets you reduce the force.  So one that was too strong also might damp motion too much and cause lost steps.  I'd lower the head on a bathroom scale and see what it weighs, then push the gas spring against the scale and see how that matches.  If it is too far off it may very well be the problem.

I added a gas spring on my machine when the new spindle motor cause the head to drift downwards when powered off.
Re: Am I loosing Steps, and what should I do
« Reply #31 on: July 22, 2016, 04:34:49 PM »
OK russh I've read somewhere that using the sherline 1/2 stepping option and changing the pulse widths on the ports and pins setup page helps control problems with stepping faults on Chinese machines.
I'm out of my depth on this subject but someone on the forum with that knowledge might be able to help, then again I might be barking up the wrong tree.
PS I'm also in the UK, a Brummie

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #32 on: July 24, 2016, 08:14:31 PM »
Russ,

Since you have a scope, could you hook it up to the step input pulse on one of your stepper drivers? Just select a federate of lets say 1000 and see how the pulses look going into your step driver. Connect the scope to the pulse - and pulse + input on your driver. Take some pictures how the signal looks like, it should be a nice stable square wave. since you are having problems on all 3 axis, it does not matter which axis you select, would be good to check all 3 axis and show us how the pulses look like.

G21

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #33 on: July 25, 2016, 04:56:52 AM »
Many thanks to all.

I will check out the gas spring as recommended.

Jim - I will do a little reading on your suggestions, also a fellow brummie (work in Great Barr)

G21 - Can I just confirm which wire is the step input pulse. (DIR-, DIR+, PUL-, PUL+, ENA-, ENA+)?

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #34 on: July 25, 2016, 10:23:43 PM »
Russh,

The step input are the Pulse - and the Pulse +, Dir - and Dir + are the direction inputs which seem to work fine and the ENA - / ENA + are the driver enable signals which also seem to work since you can move your axis around.

Since you are gaining steps, the driver must think there are additional pulses coming from the Pulse inputs to be able to make steps. If there is noise or just a bad Pulse signal coming from your card, this could be the reason for irregular and uncontrolled steps. If the signals look nice and clean, stable without much fluctuation then I start to worry about your USB card in the machine. There are quite a few machines out there by now that use the same configuration as yours and run without problem so there must be something wrong with your hardware from the moment you got yours or the computer / USB cable to control the machine maybe the culprit.

Step by step and we will figure this out.

G21
Re: Am I loosing Steps, and what should I do
« Reply #35 on: July 26, 2016, 12:45:33 PM »
I'm not that experienced with CNC setups but I had a simmilar problem with my Router losing/gaining steps. Turned out to be motor resonance or ringing caused by excessive current drive to the motor. My machine also uses Nema 34 motors and Leadshine HM860H drives, I had to reduce the drive current to less tha half what was set by the manufacturer and now all is perfect. I've no idea if this could be the cause of your problem but could just be worth a try.

All the best, Bob.

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #36 on: July 26, 2016, 10:37:31 PM »
cncbouk,

You have a good point here, since we don't know anything about the motors the current settings could be wrong. In Russh current set-up according to the pictures posted earlier, the motor current is set to the maximum of 6A per motor and 7.2A peak. I attached a little screen-shot of the dip switch settings per the manual for his drivers.

Definitely worth trying to reduce the current and see what happens.

If all the signals to the drivers are correct and clean and power supply is good, the driver / motor has to be the problem as Russh already rules out mechanical problems if I am correct.

Give it a try and see what happens.

G21

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #37 on: July 28, 2016, 07:45:07 PM »
Hi All,

Only just picked up the latest two posts so didnt try that out yet, but definately will.

Anyway, Ive spent this evening running a series of tests, checking over the electronics and also some mechnicals

Firstly, I have now stripped back all the electronics, such that I am now left with only the Z axis drive gear, the controller, and the power system. All other axis drivers have been disconnected and removed, the front panel connections have been removed etc.

So I thought I would start with a simply test, and that was to change the USB lead. I went and got a decent shielded USB lead and double checked the contiuity of the outer sheilding to the connector housing. Unforunately, this changed nothing.

I then went over all the remainging electrics, checking for any loose connections and tighting everything up to ensure all was so. I again ran a Z axis test and the same results.

Next, I took a look at the mechanical couplings from the motor to the ball screw. Ive checked these previously, but wanted to be doubly sure. I marke up a line between all the connections. I re-ran a test and the same result. Having checked the mechanical connection, the line was still intact along all connection points. So This rules out any slipage in the couplings.

So, out of ideas, I thought I would play around with the acc. and Vel. settings in mach 3. I started very very low and slowly worked back up. However, the test program I ran only moved the Z axis through a distance 70mm (reoccuring) so Im wondering if at the very low acceleration range if the motor every got up to the velocity?
Anyway, these are the results of those tests
Original Settings - Velocity: 6000, Acceleration: 300
Velocity: 500, Acceleration 20 - Good Result, Held Zero
Velocity: 2000, Acceleration 20 - Good Result, Held Zero
Velocity: 4000, Acceleration 50 - Bad Result, Lost Zero
Velocity: 4000, Acceleration 20 - Good Result, Held Zero

So it seems that if I slow the acceleration down to painfully slow, it stabilises. Im not sure this is a solution though, more an observation, as I know there are the same machines out there running fine at the orignal setting, but maybe this test can help to highlight some possible issue.

And Finally, an observation that I feel I need to mention, and Im very much wondering if this could lead us on right path to finding the issue. While I was messing with the Velocity and Acceleration settings, I forgot to compensate for this while jogging the Z axis downward. As such, I ended up crashing in to the workpiece. What I observed (which I assume is a common action) is that the motor and ball screw continued to rotate, and instead the slipping must have occured at what I think is called the Ball Nut.
What happened was that because the motor was still turning, Mach 3 thought the z axis was still travelling downward. Therefore, when retracted, the Z zero point had changed and was above the workpiece (same results).
Could this be a possible reason to whats happening durning a program run, could the Ball Nut be slipping?
The only thing I cant answer is how this would be happening on the X and Y axis as well, but concentraiting on the Z for now.



BVy the way, this is the signal from Pulse + pin
Re: Am I loosing Steps, and what should I do
« Reply #38 on: July 28, 2016, 08:25:10 PM »
No way should the screw have continued rotating unless the ball nut managed to turn as well. So that could be the source of your problem. If the ball nut turns at all it will appear as lost steps. Check the ball nut mounting method.

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #39 on: July 29, 2016, 10:43:03 AM »
The ballscrew should not continue to rotate after your head crashed and stopped. Are you sure the screw kept on turning or did you just look at the screen at Mach 3? Mach 3 will continue to run and the DRO's think the machine is still moving although the actual motor is stopped, blocked or whatever. With the head locked or blocked, the ball screw cannot turn much, maybe a few degrees due to the screw bending and the nut pressing the balls into one side of the grove.

Secondly, the signal you show on the pulse + pin does not make sense to me, did you hook up the scope correctly? Pulse + to scope A in and scope ground to pulse -. you should see a nice square wave and not what you see right now.

If you want to verify the motor turning with the head blocked, why don't you purposely block the head by moving it down to the (scrap) workpiece and see if you can slowly lower it more by jogging the Z down slowly! and watch if the motor is actually turning with the screw turning also? Since you already crashed it and saw something funny, this would confirm it. I think the couplers would slip or the motor would stall out but the screw wont turn more then a few degrees.

G21.