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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Abbreviations
- B :
-
Equivalent damping ratio [Nm]
- ids, iqs :
-
Stator current ind, q direction [A]
- imr :
-
Magnetized current [A]
- J :
-
Equivalent inertia applied to the motor
- axis :
-
[Nm2]
- Lm :
-
Mutual inductance between stator and rotor [H]
- Lr :
-
Inductance of rotor [H]
- p :
-
Number of poles
- Rr :
-
Resistance of rotor [ ω ]
- Tc :
-
Cutting torque [Nm]
- Te :
-
Electrically generated torque from the spindle motor [Nm]
- Tfco :
-
Coulomb frictional force with no load
- Tt :
-
Total torque applied to the motor [Nm]
- δTf :
-
Increment of the frictional torque due to cutting torque increment
- δTfc :
-
Increment of the Coulomb frictional torque increment due to cutting torque increment
- δTfv :
-
Increment of the damping torque due to cutting torque increment
- λdr, λqr :
-
Magnetic flux of rotor ind, q direction
- λr :
-
Magnetic flux of rotor
- ω, ωr, ωsl :
-
Synchronized, rotor and slip angular velocity of the spindle motor [rad/sec.]
References
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Tae Kwon, W., jun Hong, I. Estimation of the cutting torque without a speed sensor during CNC turning. J Mech Sci Technol 19, 2205–2212 (2005). https://doi.org/10.1007/BF02916460
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DOI: https://doi.org/10.1007/BF02916460