Possible reasons for following symptom?

Hello wise community-oracle :o)

as stated in other threads I owned a portal cnc mill. I was able to configure LinuxCNC whenever there was no documentation available so the machine is doing what I expect....so far.

No I am wondering about the following:

As soon I configure more than 10mm/s movement on the X-Axis it runs only without issues forward. When changing the direction back heading to zero it stucks sudden after short movement. Motor for X-Axis is buzzing. When it runs for some cm I can force the symptom by pressing a finger against the bridge for the Y-Axis. So it feels like the motor has enough power moving forward but not backward.

Some details about the machine can be found here

The important summary for this symptom:

X-Axis:
Nanotec Type 4H5618C 0108
Steps per revolution 200
de.nanotec.com/fileadmin/files/Datenblae...toren/4H5618_L_C.pdf
3,4 V
2,85 A
1,8 DEG

X-Axis (2 screws) Belt driven (1:2 / 15:30 teeth)

Ø 6 / 6 mm
length 19 / 19 mm

The lead pitch screw is 4mm and the portal is using a simple screw nut (no ball screws). However, with 10mm/s the X-Axis is moving wel backwardl with power and I can not stop it by just pressing a finger on the bridge. But since the X-Axis is moving forward with 25mm/s well I expect that this should possible for backward direction as well.

Would another stepper motor with more power (e.g. 8Nm) help to solve this issue? If yes, can someone recommend one which has a drive shaft of 6mm?

Regards
Michael

I would check for racking or mechanical binding first.
Then dramatically reduce your acceleration to see if problem continues.

Rick G

this i would say is a missconfiguration issue , probably you have the settings way too high for the system to handle

can you give us what power supply your using and also what stepper drivers , perhaps post your hal and ini files too
so we can see how it is currently configured .

As Rick says , cut your values down by half and see what results you obtain

Thank you for the hints. Regarding the voltage I will measure the power on the stepper connection this evening. Good hint, thanx! Maybe the voltage / ampere is not at that level when the X-axis is moving backwards by any reason.

Regarding mechanical issues: How should I figure that out? As long the stepper motors are powerless I can turn the screws in both directions.

I personally would prefer to change the stepper for the x-axis with a one which has more power. But unfortunately I was unable to find one which has roundabout 7Nm at 4A with a shaft of 6mm. So if someone has a good recommendation.... I would really appreciate a hint. Checking the chart for the nanotec motor it looks not that good (whenever it seems to be enough for the forward direction.

But of course: I should first clearify if the power is constant.

Regards,
Michael

cncbasher wrote:

As Rick says , cut your values down by half and see what results you obtain

Hello cncBasher,

Thanks for your comment!

I will post my complete configuration this evening.

Regarding cutting the values down:
Playing with driver settings did not make any changes. Between 500 and 8000 (any value) no changes visible / hearable.

II will update my initial thread with more details about power supply, stepper drivers later too. I post here when it's done.


Regards,
Michael

You should setup the step/dir timings to relaxed values first. Let's say 30000nsec direction setup/hold, 15000nsec step time.
Then, decrease axis acceleration. Start with something like 250mm/sec^2 (uh, 10 in/sec^2), you can always work up from there.
Next, choose a suitable maximum speed. Around 2000mm/min would be a good start.

You can do all this from within Stepconf and use the 'test axis' button to try the values.

Here is the config from my redZora



DaBit: Thank you for your comment. I already tried to play around with the driver times. No changes. The current config is running nearly smooth with 50-100ns. But the same issue: With 18mm/s the X-Axis is moving well in both directions. 2 mm/s more and the X-Axis will always block wehn moving backward.

I doubt this is more a mechanic issue.

More later... I have to serve my family now

Edit: The driver card for X-Axis is the HP-Step 1.5b: www.mechapro.de/pdf/hpstep_15b_en.pdf


Regards
Michael

Here are further results:

I spend this morning further time in testing the driver settings. It makes, far as I can see, no difference when I set the timings to 50 ns or to 3000 ns. I started from 3000ns and decreased the values by half stepwise. The machine is always behaving the same way.

The issue seems very likely only being related to the backward moving and feels like that the motor does not have enough power. So I have to measure the V & A of the x-axis stepper motor when moving forward and moving backward i guess. If I see that there is a difference the problem may be clear. The fact that the X-axis is moving forward with 25mm/s without issues but backward only with 10mm/s makes me wonder that this should be a driver settings issue since the driver has no specific parameters for forward / backward moving. Or did I miss something?

To be more precise: In the StepConf wizard i go into the screen for configuring X-Axis and select "Test". I leave the default 25mm/s for velocy, select a range of e.g.+ 300 mm and hit run. The X-Axis is now moving quickly forward. When the 300 mm where reached the X-Axis is turning the direction backwards and few seconds later, after some cm of moving, the x-axis is sudden blocked and the stepper motor becomes noisy. If I change the velocy to 10mm/s the test runs successful until I stop it without issues. But slow....

If I set the velocy too high, e.g. to 35 mm/s I see that the forward moving is blocking in the same way, but with no delay.... the axis is not moving but being blocked with a noisy stepper motor.

This is all information I can provide for the moment.

Regards,
Michael

I did not say 50ns, nor 3000ns. Those timings are usually far, far too tight.
Start with 15000ns (fiftteen thousand) timing for the step pulses and 30000ns (thirty thousand) timing for direction setup/hold, and leave it there until things work as expected. Once it works as expected, you might try to decrease the timings to 10000ns (note: ten thousand, not one thousand) for both step pulse/space and direction setup/hold in order to gain a little higher step rate, but not below that 10000ns unless you know what you are doing and why.

Also setup your stepper drives to 1/8 steps (both JP1 and JP0 closed), and leave it there until things work as expected.

If there is a significant difference between speed forward and backward with a low 250mm/sec^2 acceleration and correct step timings , the problem is almost certainly mechanical.

Measuring current and voltage to a stepper motor makes no sense if you don't know what to look for.