Monitoring of Slowly Progressing Deterioration of CNC-Machine Axes

  • E. Uhlmanna
  • E. Hohwielera
  • C. Geiserta

Feed axes of CNC-grinding machine tools belong to the most mechanical stressed components of machine tools due to high process forces and the rough manufacturing environment. The resulting wear and tear depends strongly on users’ product range and the manner of machine operation. To counteract a functional deficiency of these central machine units preventive maintenance activities have to be done. Manual inspection of feed axes is complex and time-consuming. An aggravating fact is that the deterioration normally progresses very slowly and its characteristic depends on the physical location at the axis. Existing approaches for automated estimation of feed axis’ “health status” do not take this factor into account.
In this paper a procedure that closes this gap is presented. During the execution of a simple test routine drive current, axis position, and feed rate are recorded. With the help of additional machine data characteristic values are computed directly at the computer of the human machine interface (HMI). The results are then transferred to and stored on a database server at the machine manufacturer. This approach enables the service technicians to trace the progression of the axis’ “health status” over a long time. Using this approach, it will be possible to detect trends within the characteristic values at a very early point in time.

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Submitted by Brousseau on Tue, 04/07/2006 - 6:45pm.

I expect that the monitoring of the deterioration of CNC-grinding machine axes should be a topic of important interest for machine tool manufacturers. Are you aware of any developments in that direction that use artificial intelligence techniques (such as neural networks or inductive learning for example) for predicting the feed axes future health status?

Emmanuel

Submitted by Geisert on Wed, 05/07/2006 - 3:03pm.

Since AI techniques are suitable for modelling of complex technical systems and for classification problems they are widely used in the area of machine diagnostics.
But at least there is a big lack of access of data for feed axes condition monitoring and prediction. Within the research project DYNAPRO we analyse feed axes health status by using position and drive current data.

Submitted by Brousseau on Thu, 06/07/2006 - 9:47am.

Thank you for your reply,

Does it mean that the data about position and drive current are not enough to constitute a valid input to AI techniques and that more data would be required but those are difficult to obtain?

May I also take this opportunity as a co-chair to encourage you to upload your presentation similarly to what Hosein Marzi did in our session:

This should benefit your work by making it even more attractive and accessible to the visitors of IPROMS2006.

Emmanuel

Submitted by Geisert on Tue, 11/07/2006 - 1:26pm.

In addition to the drive current and the position you'll need to access the velocity to make the data analysis well-defined. In the special case of grinding machines with greatly varying tool parameters (material, diameter) we also have to take into account ambient conditions like deviating tool masses.

But what I really wanted to say is that it is very hard to obtain data not only from test beds but also from machines that are used in real industrial processes.

Best Regards
Claudio

Submitted by Mekid on Wed, 12/07/2006 - 5:31pm.

I think the key procedure required for positioning accuracy maintenance will be periodical automatic calibration of different axes. This means that you have to assess both your axes and the controller. However, this is very difficult in most already made machine tools as you mentioned.
SM

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