A chatter detection method for grinding was presented in the article. The method exploits a significant change in grinding dynamics introduced by the onset of chatter. A non-linear characteristic, coarse-grained entropy rate (CER), is used to distinguish between chatter-free grinding and chatter. The method was tested on experimental data recorded in outer diameter plunge feed grinding. Calculated from fluctuations of the normal cutting force, normalised values of CER close to zero reliably indicate chatter. There are several properties of the proposed method rendering it useful for on-line automatic chatter detection in grinding: (a) The method requires no a priori knowledge about the eigen-properties of the machine-tool-workpiece system. (b) Chatter is detected regardless of the associated chatter frequency. (c) Only a scalar value has to be monitored. (d) Since CER can be normalised to the interval [0, 1], a threshold value for chatter detection can be set. Based on the experimental data available, a value of 0.1 was found to be suitable for this purpose. (e) Chatter can already be detected in its early stages, perhaps even before the machine operator can recognise it. When chatter is caused by grinding wheel wear, early chatter detection enables the operator to dress the wheel before the workpiece is severely damaged. (f) CER can be calculated rapidly, so the data acquisition procedure may in fact be more time consuming than the data evaluation itself
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