Rapid moves

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6 years 4 months ago - 6 years 4 months ago #170662 by Andy123
Rapid moves was created by Andy123
Hello,

Need some advice on setting rapid moves.

I have old CNC router that is running version 2.6.11 for many years without any problems.
It uses 1.25mm screws, NEMA 17 motors, drivers with 1/8 step.
Scale is set to 1280 (200*8/1.25). Base Period is set to 50000 ns. Acceleration 200, Stepgen ACC 250.
For many years fast moves were limited to 14mm/sec (840mm/min) for each axis.
Anything more than this would create following error. I never bothered to fix this.

Now I opened the Following error from 1 to 100, changed base period to 35000.
Following Errors are gone and I can move X, Y or both up to 20 mm/sec in MDI mode.

But once I run the actual NC program, X or Y axis stalls on some rapid moves making loud buzzing noise, then picking up moves without any issues but at the incorrect place.
It works better at 18mm/sec than 20, but not 100%.

So I thought that my drivers may not give enough current.
I changed settings peak limits from 1.7 to 2.2 to 2.7A and saw no changes.
I switched from 4A 28V power supply to 8A – no changes.
I actually measured PS current and it never go above 0.9A.
Also tried 1/4 step and different driver – no improvement.

I was playing with base period – I can easily go down to 20000 and it makes no change.
At 19000 I am getting real time delay errors.
I tried a faster computer - same results.
I also changed both ACC values up and down – still same issue.

One thing I need to mention is that its failing moves that use calculated values.
Calculations are simple +/- using 2 – 3 parameters, nothing fancy.
I am running out of ideas, so I am looking for help.
Last edit: 6 years 4 months ago by Andy123.

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6 years 4 months ago #170663 by tommylight
Replied by tommylight on topic Rapid moves
Well, nothing will help with that setup as at 14mm/s the motor is doing over 660RPM per minute, and stepper motors do not like that.
Changing the screws to 1204 or 1605 would improve speeds a lot.
Stepper motor usable torque is under 200RPM, and it drops down like a rock above that.

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6 years 4 months ago #170664 by Andy123
Replied by Andy123 on topic Rapid moves
I did not think about max stepper speed. I thought it can go over 1000 RPM :)
Changing screw on this machine is another option that was thinking about. Vendor is offering 8mm pitch replacement.

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6 years 4 months ago #170695 by Todd Zuercher
Replied by Todd Zuercher on topic Rapid moves
The only thing that might increase your top speed would be increasing the voltage to your drives and motors. (current should not be the limiting factor.) You need higher voltage to overcome the back EMF of the motors.

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6 years 4 months ago #170704 by Andy123
Replied by Andy123 on topic Rapid moves
How high should I go with voltage?
Drivers are rated 42V.
The power supply I have can't go above 28V (24-28).
I have another 5V 5A power supply that I can add quickly in series to see if it will make a difference.

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6 years 4 months ago #170725 by Andy123
Replied by Andy123 on topic Rapid moves
I did a quick test at 33.5V and was able to run at 20 mm/sec
But when I tried 22 mm/sec it failed.
I don't have power supply to go any higher, and really can't use this setup with two supplies permanently.
Unless someone can offer something else to try, I will stick with 18 mm/sec and 28.5V.
Thank you.

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