Estimation of the Cutting Torque Without a Speed Sensor During CNC Turning

  • Kwon, Won-Tae (Department of Mechanical and Information Engineering, University of Seoul) ;
  • Hong, Ik-Jun (Department of Mechanical and Information Engineering, University of Seoul)
  • Published : 2005.12.01

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 $2^{nd}$ 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.

Keywords

References

  1. Choi, Y. J., 1997, 'A Study on Cutting Force Estimation using Spindle Motor Power,' M. D. Thesis, Seoul National Univ., Seoul, Korea, in Korea
  2. Chung, D. H., 1993, 'Speed Sensorless Vector Control of Induction Motor for High Performance Control,' Jour. of Institute of Electronics Engineers of Korea, Vol. 30-B, pp. 1085-1094, in Korea
  3. Huh, K., Lee, K. and Kim, J., 1999, 'Development of a Cutting Force Monitoring System for a CNC Lathe,' Jour. of KSPE, Vol. 16, No. 1, pp. 219-225
  4. Lee, K., Jung, J., Kim, J., Huh, K. and Kim, J., 1998, 'Development of a Cutting Force Monitoring System for a CNC Lathe,' Jour. of the KSPE Spring Conference, pp. 440-444
  5. Mannan, M. A., Broms, S., 1989, 'Monitoring and Adaptive Control of Cutting Process by means of Motor Power and Current Measurement,' Annals of CIRP, Vol. 38, pp. 347-350 https://doi.org/10.1016/S0007-8506(07)62720-6
  6. Park, J. J. and Luca, S., 1994, 'Cutting Torque Estimation using Spindle Power Measurement,' Trans. of NAMRI/SME, Vol. 24, pp. 85-90
  7. Stein, J. L., Colvin, D., Clever, G. and Wang, C.H., 1986, 'Evaluation of DC Servo Machine Tool Feed Drives as Force Sensors,' ASME J. of Dynamic Sys. Meas. and Cont., Vol. 108, pp. 279-288 https://doi.org/10.1115/1.3143795