Strong vibrations in ball screw linear actuator - is it normal

**mbridge87** · 01-01-2021

Hi,

Happy new year,

I've got a linear actuator which I'm using for motion control video, not cnc. I've noticed that at slow speeds there can be a huge amount of vibration going through the machine, so much so that I can feel it standing a few feet away. Is this normal?

This is what I have - https://www.fuyumotion.com/heavy-dut...robot-arm.html

It's 1000mm long.

Would love to hear thoughts.

Thanks,

Max

**Neale** · 01-01-2021

If it is stepper motor driven, then it could be that it is not using micro-stepping. The positioning accuracy given suggests this - you might expect higher resolution with micro-stepping. However, more to the point, stepper motors driven without micro-stepping, whether you need the resolution or not, can sound and feel like marbles in a cement mixer. Depending on the mechanical setup, this might be worse st slow speeds where there is little flywheel effect.

Only guessing - difficult to tell without hearing/seeing!

**m_c** · 01-01-2021

Is it stepper or servo driven?
That webpage mentions both.
And what kind of drive is powering the motor?

I suspect it's suffering from some kind of resonance.

**mbridge87** · 01-01-2021

Thanks for the replies. It's driven with a stepper motor and a dm542t stepper driver from stepper online.

The micro stepping is set to 3200.

I can record a video tomorrow and add a link here if that would help?

**mbridge87** · 02-01-2021

Hey everyone. So here's a video which shows the vibration issue:

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

As I mention in the video there seems to be a sweet spot in terms of movement speed where the vibrations are really bad. If moving faster or slower than this sweet spot it seems to be ok. I experimented with different micro step settings a week ago and this didn't seem to make a difference, although this was before I realised there was this sweet spot and so I may test again.

The motor is hooked up to this driver, it's a 3DM2283T.

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

Would love to hear your thoughts.

Thanks,

Max

**JAZZCNC** · 02-01-2021

I don't think that's anything to do with the stepper motor. It sounds like a mechanical resonance, to me something is loose or badly misaligned. Bent ball screw perhaps.?

**mbridge87** · 02-01-2021

Oh no. That's gonna be tough to go back to the supplier with. I bought this from a Chinese company in July (ish) but have been building the whole machine from then until now so I've not used it much....perhaps it was broken on arrival?

It's quite an expensive part to replace on my own right?

**Doddy** · 03-01-2021

As always - isolate the problem - looks a fairly heavy set-up(?) but could you lift it from the wooden stands to verify that the noise is local to the slide table? (and not resonance from the stands)... I think unlikely - but a cheap test.

What's interesting with the video - from 02:40, the noise appears co-incident with the rotational position - would like the OP to verify this - from the short clip - seems to be the same bit of the motor coupler visible when the noise is at it's loudest - so is this a bent screw?, some mechanical foul along the motor/screw axis?

Does the problem remain with the (weight of the) camera mount removed? If not, does the problem remain with the bed fully supported? (can it be dropped onto the ground, or lifted onto a table?)

Next thing for me would be to remove the panels from the bed. Or to decouple the motor from the screw and to manually assess the freedom of rotation of the screw (decouple from the motor-side, and thumb/forefinger rotate the coupler)

**JAZZCNC** · 03-01-2021

Originally Posted by mbridge87

Oh no. That's gonna be tough to go back to the supplier with. I bought this from a Chinese company in July (ish) but have been building the whole machine from then until now so I've not used it much....perhaps it was broken on arrival?

It's quite an expensive part to replace on my own right?

I wouldn't be rushing it back just yet based on my quick observation, identify the problem first.

My main point was I'm quite sure it's not resonance affecting the motor for the following reasons.
#1 It's not spinning fast enough
#2 It's a 3 phase motor on a digital drive so it's highly unlikely
#3 It's fastend firmly with a good strong mounting.

Eliminating the motor/drive and from the sounds it's making everything points to alignment, binding or bent ballscrew or rails even.?

I don't know what's under those covers in terms of rails or ballscrews but if it's using precision linear rails then any twist or misalignment could cause binding that will result in vibrations and because of the size of the motor it won't stall but rather just power past it increasing the vibrations. Also, the wooden frame it's sat on looks a little "heath robinson" so could easily be putting the stage into twist.?

This is the problem with precision equipment, if the rest of the setup doesn't match it's pointless. I would set the whole stage down on a flat surface and make sure it's fastened securely.

**m_c** · 03-01-2021

I'd like to know the inner workings of that actuator.

Given the lack of detailed information about it, I'm going to guess it's probably not using that good a quality linear slide which has some play in it rather than being preloaded, which is then being amplified by resonance probably triggered by some runout in the ball screw.
Your setup will be adding resonance due to it's centre of gravity away from the slide, so any play in the slide will be amplified.

What happens if you press down, and put a load on the slide as it moves?