Strong vibrations in ball screw linear actuator - is it normal

[mbridge87]

Hey everyone,

Thanks so much for the help so far. I’ve contacted the company I purchased this from to see what their opinion is. In the meantime, here are answers to all your questions:

1) The noise still persists when taken off the table. The table is extremely strong and sturdy and the slider was held down with G clamps but it was worth a try.
2) The noise does seem to coincide with the rotational position – see video below – I also notice that the noise seems to be worse when travelling away from the motor in the centre of the slider. In addition, there seems to be a noise like sand/metal inside almost like it’s grinding. You may be able to hear this on the video.

https://drive.google.com/file/d/16y3...ew?usp=sharing

3) Problem does remain with camera mount removed. Problem also remains when on the floor
4) Taking everything apart will be my next step
5) The table is something I use for photography / videography. It’s rock solid, weighted down, and the slider is held in place with G clamps. It’s only temporary but I’d be surprised if it was causing any issue. I have put it on the ground and the issue persists.
6) Pressing down on the slider as it moves has very little effect. It does decrease the vibrations a little but the main nasty noise is still there.

I think that answers all the questions. Here’s another video which shows the slider moving back and forth a couple times. The noise seems to be worst in the centre of the slider when it’s moving back from the motor side.

https://drive.google.com/file/d/170V...ew?usp=sharing

Apologies I seem to have filmed that video upside down...new phone.

I think the next step is clearly to take it apart and see what’s going on. I’ll wait to hear what the manufacturer says first though.

Side note – Where is the best place to purchase something like this from? If my budget were say £700 for something similar, where would you guys go? I know £700 is not a huge amount for a ball screw slider like this.

Thanks again

[Doddy]

I also notice that the noise seems to be worse when travelling away from the motor

I think the next step is clearly to take it apart and see what’s going on. I’ll wait to hear what the manufacturer says first though.
Thanks again

Agreed with dismantling... a bit at a time. And appreciate you wanting to sanction this with the supplier first.

Interesting observation on moving the platform away from the motor (screw between bed and bearing block (or motor) in compression). My random logic would be to check on the tightness of the nut on the bearing block behind the motor coupler... or for mechanical interference in this area (or between coupler and motor - explains the rotary position association), or even if the bearing blocks are bolted tightly down. Pure speculation of course.

Of interest (and what would make me cautious with running ahead with disassembly) is how motion is achieved with the dust-proof guard in place - does that move (conveyor-like) with the table? If not (and I've read a couple of sites that intimate that a stainless steel band is fed into the carriage - around a couple of rollers... and these would require lubrication... but that would all be explained in the product literature). Again, pure speculation.

Okay, out of ideas... but watching this thread with interest.

[JAZZCNC]

Sounds like you have a few things going off here.

I'd definatley say this is something to do with the linear rails or ballscrew alignment, or bent, etc, as it doesn't take much to cause binding. Possible end bearing supports are lose or poorly fit bearings.

I'd also say because of the grinding noise, which is common with cheap Chinese ballscrews, the ballnut needs stripping and cleaning.
It's common for Chinese ballscrews to not be cleaned properly at the factory so grinding dust etc is left in the ballnut. That said I wouldn't recommend you go stripping the ballnut down without knowing a little about how they work and being prepared and setup to do it, other wise you'll have dozens of little balls all over the floor.!!

Side note – Where is the best place to purchase something like this from? If my budget were say £700 for something similar, where would you guys go? I know £700 is not a huge amount for a ball screw slider like this.

What length do you need.? I could make you something like this easy enough. PM me if you want to discuss it and I'll give you my details.

[mbridge87]

Yes, I am a little concerned about stripping this all down. I've heard people say that all the ball bearings can fall out if you're not careful.

I posted this same question in a Facebook group which is all about motion control, it's full of people with lots of experience building motion control video rigs. It's called DIY motion control for those interested. Anyway, the consensus there seems to be that this is quite common at particular speeds when using ball screws for motion control and is a resonance thing.

Now, I don't know if they're correct and I'll still be investigating this but it's interesting that they all seem to think this is normal. I wonder if using this for motion control video has an impact. For example, in that use case I think, and correct me if I'm wrong, that it would be more likely to use a ball screw at this slow speed and at more speeds in general; fast, slow etc. Whereas cnc users would generally be going a bit quicker?

I'll pop you a separate message Jazz. Would love to chat

[JAZZCNC]

I see no reason why it should judder at this speed, I can tell you without question that any decent CNC machine would easily move at this speed and slower without juddering. It wouldn't be much use if it didn't as those vibrations your feeling through your feet would show in the cut quality.

To me I can't see why if it was setup correctly without binding or anything being bent, etc, and securely fastened down why this linear stage should vibrate.

[mbridge87]

Thanks Jazz. It's great to hear from someone knowledgeable in this area.

It did surprise me that the guys in the motion control Facebook group seemed to think it was normal. I'll continue investigating things with the manufacturer and see what they say.

Given they're in China, if they suggest stripping it down is that a difficult thing to do? I imagine it would be relatively simple, the only part I'm not sure about is the ball screw part with the bearings (not sure of the name). Fingers crossed they also honour the warranty.

[mbridge87]

Hey everyone. Quick question. I double checked my current settings as I was told that this could cause some of the problem. I reduced the current and the issue improved, it didn't go away but was definitely better. The downside is that performance, in terms of speed, drastically reduced.

At the original current setting, with 32x micro stepping, I could move the slider very fast, I'm afraid I can't quantify that as I'm not sure how to measure it but with no payload I couldn't really get it to stall. At least, I got to a point where it was far faster then I'd ever need and stopped. With the slightly lower current setting it stalls very easily. Again, this is hard to quantify but not very fast.

This video shows how fast it could move at the higher current setting - https://drive.google.com/file/d/17A-...ew?usp=sharing

I'd estimate that at the lower current setting it can move at maybe 1/6th of this speed.

This is the info for the stepper motor - https://drive.google.com/file/d/1rhc...ew?usp=sharing - if that link ever breaks the model is FM86128SJT03 - it's rated at 3 amps.

I originally had it set to 3.2A (RMS) and 4.5A (peak) on the driver. I tested it quite a lot at this setting and the motor barley got warm so I thought this was ok. The next setting down is 2.2A (RMS) and 3.1A (peak). That lower setting is where the performance drops off.

Did I have the current set too high?

[Clive S]

No. It won't harm the motor, it can run hot well in excess of 50C.

Ie. re the drive what voltage can it handle. if it is 50V then use about 10% less 45V. it is the volts that matter.

What voltage are you using and what amps can the power supply give?

[m_c]

I think you might need a few things clarified.

The microstepping setting simply controls how many steps the drive takes on the input, compared to what it outputs. A more accurate description would be step-multiplier/ratio.
I'd guess the drive output will never go above 16 or 32 microsteps, as above that resolution, it makes no difference to motor smoothness, and it certainly does nothing for accuracy, as microstepping is by nature inaccurate. Due to the very nature of microstepping, what it's essentially doing is holding the motors rotor between two electromagnetic springs, so position cannot be guaranteed other than to the nearest step.
Personally, I would never run above 32 microsteps, as there is no real benefit.

In terms of current. In electric motors, current = torque. Reduce current, you reduce torque. Less torque means you can't accelerate as fast. It also likely means you'll hit the stepper motor/driver bad resonance point and stall at a lower speed.
Too high a current could cause failure due to overheating, but I'm sure you would have noticed if the motor had heated up.
As Clive says, stepper motors can run hot. 80degC after running for a long time is acceptable, but if they get that hot in a matter of minutes, then you've got a problem.


One thing you could try, is unbolt the motor, and separate it from the screw (that style of coupler will simply pull apart)
Try spinning the screw by hand, to see if it feels smooth
And run the motor with no load.


Having watched the video again, it could just be the fact it's using a big stepper motor.
It does sound like the stepper motor vibrating, and being amplified through the relatively light weight rig. There does seem to be a variation in sound level per revolution, but probably nothing you'd need to worry about.

A solution would be either a small servo, or possibly a smaller stepper motor with some gearing.
Although given you don't need high precision, I wonder if the existing motor could be mounted using some kind of anti-vibration mounts to isolate the motor vibration from the rig.

[mbridge87]

No. It won't harm the motor, it can run hot well in excess of 50C.

Ie. re the drive what voltage can it handle. if it is 50V then use about 10% less 45V. it is the volts that matter.

What voltage are you using and what amps can the power supply give?

This particular driver (linked below) connects directly to AC so it's 240vAC. It has the PSU built in unlike the DM 542T drivers I have which utilize a separate PSU that supplies 42.5 volts. I double checked and there is nowhere you can select the voltage, the manual suggests this is set automatically by the driver. Do let me know if I've done something stupid there.

https://www.omc-stepperonline.com/di...per-motor.html

In terms of Amps, this screen grab shows you all the different options.