A New Approach to the Estimation of Cutting Dynamics Using Active Magnetic Bearings

[+] Author and Article Information
Min Chen

Department of Mechanical and Aerospace Engineering,  University of Virginia, Charlottesville, VA 22903

Carl R. Knospe

Department of Mechanical and Aerospace Engineering,  University of Virginia, Charlottesville, VA 22903crk4y@virginia.edu

J. Manuf. Sci. Eng 127(4), 773-780 (Feb 13, 2005) (8 pages) doi:10.1115/1.2034509 History: Received January 22, 2004; Revised February 13, 2005

A new experimental approach to identify the cutting dynamics in turning operations is presented. This method treats the problem as a closed-loop gray-box identification problem and is based upon spectral analysis and least squares estimation techniques. An active magnetic bearing is employed both to excite the system and to increase the tool’s damping. The inherent time delay of the cutting process is “removed” in identification by limiting the observation period to less than one revolution period of the workpiece. The coefficients of several cutting tests were identified. The methodology was validated by predicting the critical depth of cut from the identification results and comparing with the experiment result measured from a cutting test.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Machining process block diagram

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Figure 2

Identification block diagram

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Figure 3

Correlation between r¯(n) and y¯(n) for NT=200 and N=200

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Figure 4

Photograph of the experiment test rig showing tool, front and rear platforms, flexures, and active magnetic bearing

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Figure 5

Experimental arrangement

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Figure 6

Comparison between free tool vibration and PID controlled tool vibration; data from impact tests

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Figure 7

Identification results: dynamic cutting coefficients vs. depth of cut. The cross marks (x) are the estimated values, and the bars represent 95% confidence intervals.

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Figure 8

Nyquist contour for Gt(1−e−Ts)

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Figure 9

Experiment validation of the chatter prediction




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