Vibration on Ball Screws

So many sources and so little information. I'd use an accelerometer.

Unfortunately, the ball screws are in a machine that no one knows all the particulars. I need to establish a criteria for measuring vibration on the ball screws with little or no information about them. We have placed accelerometers on the ball screws and established a baseline. I need generalities on where to look for problems in the frequency domain, simliar to the vibration severity chart. I am hopeful to get something like "look at 1x rotation, 2x rotation, etc."

Thanks,

John

Tell me a little more about the ball screw. Chances are the methods of measuring vibration and establishing failure criteria would be the same as that used in any ball or rolling element system. If so, there should be some pretty good sources-including the manufacturer of the bearing. Vibes

How about Laser Vibrometry?

DJ Southern Cal.

Hi,

first you should try to distingush between different error sources:

axial vibration, radial (bending) mption, pitch and yaw - motion, worn balls and screw, dirt and/or corrosion, loss of preload.

In axial vibration there are three stiffnesses:the axial bearing, the stiffness given by the length of the spindle that extends between axial bearing an nut, and the screw to balls plus balls to nut stiffnes plus may be mountings. As these are series connected the compliances add. This results in a length dependent stiffness and depending axial natural frequency. Take a measurement to see if you have your problems generated by axial vibration. Excitation is often the servo.

Similar analysis of the other possible error sources can be done: each with specific features that can be measured.

A first approach can be a measurement of vibrations with accelerometers (on the frame and on the moving mass). Make sure you get all 3 directions, and let the spindle turn fast enough to get the rotation speed inside the bandwidth. Else you will have to measure also vibration amplitudes by distance sensors.

Take this measrement on your machine and on a new machine of same type.

Start monitoring the vibration data and decide yourself (with the help of the machine manufacturer and the buer of the parts you machune) when to get a repair.

This is easy to start but requires some effort to be successful.

RHABE

Scientific and Technical Consultant

Precision Engineering and Measurement
Errors and design in sensors, bearings, materials, machining and processes