Estimation of the cutting torque without a speed sensor during CNC turning |
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Authors: | Won Tae Kwon Ik jun Hong |
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Affiliation: | (1) Department of Mechanical Engineering, Ansan College of Technology, 425-792 Kyungki, Korea;(2) School of Mechanical and Automotive Engineering, Catholic University of Daegu, 712-702 Kyungbuk, Korea;(3) School of Mechanical and Aerospace Engineering, Seoul National University, 151-742 Seoul, Korea |
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Abstract: | In this paper, the cutting torque of a CNC machine tool during machining is monitored through the internet. To estimate the
cutting torque precisely, the spindle driving system is divided into two parts: electrical induction motor part and mechanical
part. A magnetized current is calculated from the measured three-phase stator currents and used for the total torque estimation
generated by a spindle motor. Slip angular velocity is calculated from the magnetized current directly, which gets rid of
the necessity of a spindle speed sensor. Since the frictional torque changes according to the cutting torque and the spindle
rotational speed, an experiment is adopted to obtain the frictional torque as a function of the cutting torque and the spindle
rotation speed. Then the cutting torque can be calculated by solving a 2nd order difference equation at a given cutting condition. A graphical programming method is used to implement the torque monitoring
system developed in this study to the computer and at the same time monitor the torque of the spindle motor in real time through
the internet. The cutting torque of the CNC lathe is estimated well within an about 3% error range in average in various cutting
conditions. |
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