How to avoid vibration effects?

[simasa]

Hello,
I am looking forward to install a laser based measurement system on a milling machine. The purpose of measurement system will be to measure small scale relative movements of machine components or machine bed.

The measurement unit weight is about 0.8 Kg. The unit could be screw mounted on a side wall of the machine (using a 25 cm aluminium arm). When machine in working condition, the side wall of the machine may possess some vibration (I guess very low). Thus I assume it will affect the accuracy of the measurement system.

Any suggestion to address this problem? I will be very thankful. Some approaches could be as follows.

• If I use some rubber dampers between side wall and arm, the unit may lose rigidness/stiffness.
• If I use separate mounting for the unit independent of the machine, it shall not be smart solution. There will also be a need of massive mechanical design.
• One solution may be using acceleration sensors at the other end of the arm to measure and compensate the vibration effects (not sure it could be a potential solution).


Any secession would be very welcoming. Thanks in advance.
Regards

simrs

 

[IRstuff]

Actually, I think you need to go the other direction and make the mounting MORE rigid, not less. Vibration isolation implies removal from the vibration, and hence, the actual position of the machine, but you're supposedly trying to measure the position of the machine relative to something else.

I also question why you would mount the measurement unit on a wall. Walls, by design, are not supposed to be rigid in one axis, thus introducing motion that may have nothing to do with the motion of the system as a whole. If the wall is oilcanning, then the motion is hardly representative of the machine's motion.

TTFN

FAQ731-376

 

[simasa]

Thanks for a very helpful answer. Yes, I understand that I should make the arm of the machine more rigid. Currently it is 20x57x280 mm3 aluminium, fixed with 6 screws on machine wall. The Wright of measurement system is about 0.8 Kg attached to the other end. But I have no idea is it is rigid enough.
The length of 280 mm may amplify the vibration effects due to bending in arm. But I am not sure if it would be of considerable size.


The machine structure is of granite. The wall where measuring unit would be mounted is actually side wall (metallic) of spindle housing. I choosed it because it seems to be only suitable and potential possibility.
I understand your point that the vibration/oscillation may not represent the motion of the machine. Then it seems to be unsolved problem. Could you have some more suggestion ?

Regards

simrs

 

[snoopnoon]

Does it have to be a laser measurement system? Can a LVDT be precise enough for your application?

 

[IRstuff]

I think that you know what you need to do. A wall is almost always attached to a rigid structure. A triangular truss is stiffer than a single element.

Additionally, you should look at how other people with similar systems deal with this type of measurement.

TTFN

FAQ731-376