Estimating cutting force from rotating and stationary feed motor currents on a milling machine

The feed motor current of a machine tool contains substantial information about the machining state. The current has been used as a measure of cutting forces in much previous research; however, this indirect measurement of the cutting forces was feasible only in a low frequency range up to about 60 Hz when milling machining. In this paper, the bandwidth of the current sensor was expanded to 130 Hz. The unusual current behavior between 45 and 60 Hz was examined and analyzed. It is necessary to estimate the cross-feed directional cutting force that is normal to a machined surface, since it directly affects the error of that surface. However, because of the undesired behavior of the stationary motor current, difficulties are encountered when using it to estimate the cutting state. An empirical approach was used to resolve this problem. As a result, we show that the current is related to the infinitesimal rotations of the motor, and it is this that causes the undesired behavior of the current. Subsequently, a relationship between the current of the stationary feed motor and the cutting force normal to machined surface was identified with an error of less than 20%. (C) 2002 Elsevier Science Ltd. All rights reserved.