Novaturn 1997 X axis losing postion.

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TimPower
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Novaturn 1997 X axis losing postion.

Post by TimPower » Fri 02 Nov , 2007 17:34 pm

Hi there,
I won't use the machine till I can sort out the turret however I was using tool post 3 to run a few programs with just a roughing tool. I'm having a problem with it though losing it's X postion. On one program the first cutting move takes the tool in a facing operation from X30 Z0 to X0 Z0 then rapid out to X30 Z0 but when it attempts to return in rapid mode there is a high pitched noise from the motor. The machine reads that is has returned to X30 when it is actually around X2 or X3. It only happens in G99, when I switch to G98 and substitute in F1000 it's fine. Have you come across this before, is the encoder in the X motor easily serviced or do you think there is something else up with it? As I'll be cutting threads I'll have to run in G99.

Cheers,
Tim.

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Diagram of X axis setup.

Post by TimPower » Wed 02 Dec , 2009 13:22 pm

Hi there,
I'm trying to get back to this problem I'm having with the X axis losing position. I gave up on it last time as it itook up too much time. It mainly occurs when using a G99 and especially if the X direction is reversed quickly, not so much on a G98 for some reason. Also sometimes when the X goes home a high pitched noise is emitted (spinning motor?) and I have to E stop, its gone when I release the E stop. I wish to examine the lead screw for damage before tensioning the belt and would like any tips for disassembly or a drawing of the assembly would be better. Also any tips on re-assembly of the guide on the dovetail guide would be handy or pitfalls to watch out for.

Cheers,
Tim.

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Re: X axis losing postion.

Post by Denford Admin » Thu 03 Dec , 2009 10:28 am

Hi - sorry your original post was missed ! :oops:

Anyway, what machine is it ? Is it DOS software / real Fanuc control / VR windows software etc...

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Re: X axis losing postion.

Post by TimPower » Thu 03 Dec , 2009 10:39 am

No bother DA,
It a 1997 Novaturn running on V1.22.
Leadscrew okay. I pulled the X stepper out and ran it in my hand. In the higher speeds it stops intermittantly while the display keeps going. I'm thinking that the pulses are being counted but that the control is open loop so once a pulse is sent to the stepper, the control assumes that the motor will move to this position. Have you come across this problem before? Before changing the stepper motor what characteristics should I look for if I connect a scope to the motor input just so I can rule out a board problem?

Would be very grateful for any help.

Rgds,

Tim.

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Re: X axis losing postion.

Post by Denford Admin » Thu 03 Dec , 2009 11:56 am

This link may help
http://www.piclist.com/tecHREF/io/stepp ... ni_wks.htm

For the cost of a new stepper motor, I'd be tempted to try a new one anyway - they're a lot more efficient and have better torque curves than they had 10 years ago.

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Re: X axis losing postion.

Post by Steve » Thu 03 Dec , 2009 18:24 pm

Steppers genrally have lower torque as they run faster.

Testing one while it is disconnected may not prove too much as they also have resonant frequency bands that can cause them to stall offload.

If the stepper is working at lower speeds it is unlikely to be faulty. When a stepper does stall it will loose steps and be out of position.

I would test that the belt is tight and that the mechanics are not too tight.

A newer motor may have a bit more torque but it sounds to me like the mechanics have changed.

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Re: X axis losing postion.

Post by Martin » Thu 03 Dec , 2009 21:54 pm

When you updated to version 1.22 did you upgrade/update the control card/eprom?

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Re: X axis losing postion.

Post by TimPower » Fri 04 Dec , 2009 11:41 am

Steve, thanks for the info. The ball screw runs fine and slides are well oiled.
Martin, I just downloaded the software for V1.22 and popped in my old registration disk when asked. I didn't know I had to make any other changes. Am I missing something glaringly obvious here with the Eprom?

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Re: X axis losing postion.

Post by Denford Admin » Fri 04 Dec , 2009 11:50 am

I think Martin is wondering if the software has some different parameters setup. It could be that the machine is being run too fast for it's capbilities.
If you limit the machines maximum feedrate in parameters, you will hopefully keep the motors within the best highest torque curve.

Did you also check the leadscrew for backlash? (in the nut) or endfloat (where the screw slides in and out of the end bearings)

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Re: Novaturn 1997 X axis losing postion.

Post by TimPower » Fri 04 Dec , 2009 13:35 pm

No, it's not a backlash issue. I took off the guard at the top of the X and put a mark at the top of the stepper shaft. When the problem occurs the X axis counter continues to count till it gets to the desired value but the shaft is not moving during this time.
For instance lets say I put in a 30mm diameter billet and run a simple facing and turning program with G99
N10 T01 S1500 M03
N20 G00 Z1 X30
N30 G01 Z0 F0.05
N40 G01 X0
N50 G00 Z1
N60 G00 X29
N70 G01 Z-20.

When I try this, the tool comes in as normal, faces but when it goes into rapid it moves a couple of mm then the stepper stalls but the counter continues to X29. Then it continues with N70 resulting in a crash as its actually only at X4 or X17, etc. - it doesn't stall in the same place every time.

I checked the Eprom, its V2.1 on a smartstep/3 board. Is this compatible with V1.22? If not can anyone tell me what is the latest software than I can use with this chip?

If someone can confirm the software for me I'd appreciate it and I can try the machine at lower speeds. I can put the rapid right down and keep the speeds low and use molding wax billets for the demos for the students. Hopefully it will get me moving.
Thanks again for all the help.

Tim.

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Re: Novaturn 1997 X axis losing postion.

Post by Martin » Fri 04 Dec , 2009 17:06 pm

Eprom version 2.1 is correct & also the latest.

Have you lubricated the slides?

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Re: Novaturn 1997 X axis losing postion.

Post by TimPower » Mon 07 Dec , 2009 10:32 am

Yep, plenty of oil. No luck though. I thought the problem was isolated to the X axis but the Z asix is losing position too. It will lose position and attempt a tool change without going home. I'll try to upload a clip later.

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Re: Novaturn 1997 X axis losing postion.

Post by Denford Admin » Tue 08 Dec , 2009 10:01 am

If you're sure the mechanics are free to move easily, then I'd be looking at voltage levels to the stepper drives... the machines were not built for heavy duty cutting, but certainly shouldn't stall just going home.
The other thing I thought that could be setup wrong is the acceleration...not sure how to change but it's probably in the .OPT file, looking at the likes of this post:
viewtopic.php?f=9&t=2347&hilit=.opt

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Re: Novaturn 1997 X axis losing postion.

Post by Martin » Tue 08 Dec , 2009 21:04 pm

It looks loke the machine is running from VRTurning version 1.22 so there is not a OPT file. The settings are all in the machine parameters.

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