Electric motor controller comprising function for simultaneously estimating inertia, friction, and spring
A sinusoidal command is added to a torque command of a controller to acquire a velocity and a current value of an electric motor. An estimated coupling torque value is calculated by calculating an input torque value from the current value and a torque constant of the electric motor and further calculating a coupling torque value from a velocity difference, motor inertia, and the input torque. An estimated torque error is then calculated from the estimated coupling torque value and the coupling torque value, and inertia, friction, and a spring constant are estimated from the estimated torque error, the velocity, and the coupling torque value.
1. 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.
2. The electric motor controller according to claim 1 , wherein the estimated coupling torque calculating unit is configured to obtain the estimated coupling torque value based on:
a product of the estimated inertia and the difference between the velocity acquired for the current sampling period and the velocity acquired for the previous sampling period;
a product of the velocity acquired for each sampling period and the estimated viscous friction coefficient of the driven body;
a product of a polarity of the velocity acquired for each sampling period and the estimated Coulomb's friction coefficient of the driven body;
a product of a reciprocal of the estimated spring constant and a second-order difference of coupling torque values; and
a product of the estimated viscous friction coefficient of the driven body, the reciprocal of the estimated spring constant, and a difference in the coupling torque values.
3. The electric motor controller according to claim 1 , wherein
the correcting unit is configured to correct the estimated inertia of the driven body, the estimated viscous friction, the estimated Coulomb's friction coefficient, and the estimated spring constant for each sampling period by using (a) the velocity of the electric motor, (b) the coupling torque value, and (c) an accommodation coefficient so that the estimated torque error calculated by the estimated torque error calculating unit is minimum, and
the accommodation coefficient is inversely proportional to magnitudes of the velocity and the coupling torque value and has a dead zone in which the accommodation coefficient is zero when the velocity is equal to or lower than a predetermined value.
4. The electric motor controller according to claim 1 , wherein the estimated coupling torque calculating unit is configured to calculate the estimated coupling torque value based on
an estimated velocity of the driven body,
the velocity of the electric motor,
the coupling torque value,
the estimated inertia of the driven body,
the estimated viscous friction of the driven body,
the estimated Coulomb's friction of the driven body, and
the estimated spring constant of the spring of the coupling shaft.
5. The electric motor controller according to claim 4 , wherein
the estimated velocity of the driven body is obtained using
the velocity of the electric motor acquired for each sampling period,
the coupling torque value, and
the estimated spring constant at the time of the previous sampling period.
6. The electric motor controller according to claim 2 , wherein
the correcting unit is configured to correct the estimated inertia of the driven body, the estimated viscous friction, the estimated Coulomb's friction coefficient, and the estimated spring constant for each sampling period by using (a) the velocity of the electric motor, (b) the coupling torque value, and (c) an accommodation coefficient so that the estimated torque error calculated by the estimated torque error calculating unit is minimum, and
the accommodation coefficient is inversely proportional to magnitudes of the velocity and the coupling torque value and has a dead zone in which the accommodation coefficient is zero when the velocity is equal to or lower than a predetermined value.