Patent ID: 8872463

Claim:
An electric motor controller for controlling an electric motor configured to drive a driven body of a machine tool or industrial machinery, wherein the driven body and the electric motor are coupled to each other by a coupling shaft which has resonance characteristics including a spring, in a servo system including a ball screw and/or decelerator that is estimated as a model of torque from inertia, friction and a spring of motion of the driven body, the controller comprising: a command unit configured to add an M-sequence command or a sinusoidal command to a position command, a velocity command, or a torque command of the controller; a current value acquiring unit configured to acquire a current value of a current flowing through the electric motor for each sampling period; an input torque calculating unit configured to calculate an input torque value of an input torque to the driven body based on the current value and a torque constant of the electric motor; a velocity acquiring unit configured to acquire a velocity of the electric motor for each sampling period; a coupling torque calculating unit configured to calculate a coupling torque value of a coupling torque produced by a difference between motion of the electric motor and the motion of the driven body, based on a difference between a velocity acquired by the velocity acquiring unit during a present sampling period and a velocity acquired by the velocity acquiring unit during a previous sampling period, inertia of the electric motor, and the input torque value calculated by the input torque calculating unit; an estimated coupling torque calculating unit configured to estimate an inertia of the driven body, a viscous friction coefficient of the driven body, a Coulomb's friction coefficient of the driven body, and a spring constant of the spring of the coupling shaft, and calculate an estimated coupling torque value from the velocity of the electric motor, the coupling torque value, the estimated inertia of the driven body, the estimated viscous friction coefficient of the driven body, the estimated Coulomb's friction coefficient of the driven body, and the estimated spring constant of the spring of the coupling shaft; an estimated torque error calculating unit configured to calculate an estimated torque error from a difference between the coupling torque value and the estimated coupling torque value; and a correcting unit configured to correct (i) the estimated inertia, (ii) the estimated viscous friction coefficient, (iii) the estimated Coulomb's friction coefficient, and (iv) the estimated spring constant for each sampling period, by using the velocity and the coupling torque value, so that the estimated torque error calculated by the estimated torque error calculating unit is minimum.