Patent ID: 7190134

Claim:
A torsional vibration suppressing control method in an electric motor speed control system constituted by a mechanism for transmitting a driving torque from an electric motor to a load through a driving shaft which is provided on the load side of the electric motor and has a low torsional rigidity, and a control device for feeding back an electric motor mean speed N MAVG obtained by a calculation for a mean value every constant cycle for an electric motor speed detection signal detected by a speed detector for a speed command N REF and calculating a deviation signal, and controlling a current of the electric motor in order to have an electric motor torque in accordance with a torque command signal T RFA obtained by amplifying the deviation signal by means of a speed controller having a proportional gain and an integrator or only the proportional gain, wherein a signal obtained by multiplying a signal acquired by differentiating the electric motor mean speed signal N MAVG by an inertia time constant τ M of the electric motor portion is input as an electric motor acceleration torque signal T MAFB to an inertia controller with respect to the torque command signal T RFA output from the speed controller, and the inertia controller multiplies the electric motor acceleration torque T MAFB by the proportional gain and then outputs a value thus obtained as an inertia control signal T MJC through a second-order or first-order low-pass filter and a second-order or first-order high-pass filter, feeds back the electric motor acceleration torque signal T MAFB to an electric motor acceleration torque command T RFAX obtained by decreasing the inertia control signal T MJC from the torque command signal T RFA output from the speed controller, and controls a current of the electric motor in order to have an electric motor torque in accordance with a signal T RFM obtained by adding, to the acceleration torque command T RFAX , a torque compensation signal T RFL acquired by amplifying a signal of a deviation thereof by means of an electric motor acceleration torque controller constituted by the proportional gain and the integrator, thereby carrying out a control in order to cancel an electric motor load torque in response to the torque compensation signal T RFL calculated and output in such a manner that the electric motor acceleration torque command T RFAX and the electric motor acceleration torque feedback signal T MAFB are coincident with each other and equivalently enlarging and controlling an inertia of the electric motor portion.