Electricity: motive power systems – Constant motor current – load and/or torque control
Patent
1992-09-29
1995-04-25
Shoop, Jr., William M.
Electricity: motive power systems
Constant motor current, load and/or torque control
318434, 388930, H02P 700
Patent
active
054102286
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for suppressing the torsional vibration of a drive control unit for controlling the rotational speed of an electric motor in a mechanical facility which is equipped with a mechanism for transmitting a drive torque from the electric motor to a load through a drive shaft of low torsional rigidity disposed at the load side of the electric motor and, more particularly, to a method and an apparatus for a drive control unit for controlling the rotational speed of an electric motor in facilities which are equipped with a mechanism for transmitting a rotational torque to a machine through a drive shaft of low torsional rigidity disposed at the load side of the electric motor and a mechanism having a speed detector mounted on the shaft of a rotor for transmitting a rotational torque to the rotor through a drive shaft of low torsional rigidity disposed at the side opposite the load.
BACKGROUND OF THE INVENTION
FIG. 1 is a mechanical diagram showing a variable speed drive apparatus. The rotational torque is transmitted to a machine 5 from an electric motor 2 through a drive shaft 4 having a torsional rigidity of K [Kgm/rad].
A variable speed control unit 1 controls the speed of the electric motor 2 by using a signal, which is detected by a speed detector 3 attached to the electric motor 2, as a speed feedback signal.
FIG. 2 is a block diagram showing a speed control unit including the well-known torsional vibration system. As shown in FIG. 2, the speed control unit 11 has an integrator having a proportion gate A and a time constant .tau..sub.I and amplifies a deviation between a speed command N.sub.REF as indicated at 10 and a speed feedback signal N.sub.MFB to output a torque command signal T.sub.REF. When the torque command signal T.sub.REF is inputted to a motor torque controller 17, this motor torque controller 17 controls the torque of the electric motor with a linear delay time constant .tau..sub.T. Incidentally, the speed feedback signal N.sub.MFB is prepared from the rotational speed N.sub.M of the electric motor through a linear delay first-order lag element 16 (wherein .tau..sub.F : a speed detection filter delay time constant).
A motor torque T.sub.M is controlled in accordance with the aforementioned torque command signal T.sub.REF.
Reference numeral 12 designates a block indicating the mechanical time constant .tau..sub.M of the electric motor; numeral 13 designates a block indicating a torsional time constant .tau..sub.V ; and numeral 14 designates a block indicating the mechanical time constant .tau..sub.L of the load.
On the other hand, numeral 15 designates the load torque T.sub.L2 upon the machine 5, and letters N.sub.L designate the speed of the load.
In the block diagram of FIG. 2, a ramping (or linearly accelerated) speed command N.sub.REF is fed to the input. If a torsion is established in the drive shaft 4 when the motor speed N.sub.M and the load speed N.sub.L occur, a transient gain of the speed control system abruptly occurs with a mechanical resonance frequency of the rotational motion, which is determined by the torsional rigidity of the drive shaft, the inertia of the electric motor, and the combined inertia of the machine and the load. As a result, there occur periodic speed fluctuations which are detrimental to the machine facilities, as shown in FIG. 3.
As means for solving this problem, according to the prior art, a vibration suppressing filter 18 is inserted at the output side of the speed controller 11, as shown in FIG. 4, so as to reduce the transient gain at the resonance point of the mechanical system. The torsional vibration suppressing filter 18 is given a transmission function, as expressed by the following formula: angular frequency; .delta..sub.F designates a filter characteristic constant; and s designates a Laplacian operator.
In the prior art, the filter angular frequency .omega..sub.F and the filter characteristic constant .delta..sub.F, as appearing in the above Formula, and the propor
REFERENCES:
patent: 4870334 (1989-09-01), Iwasa et al.
patent: 4992715 (1991-02-01), Nakamura et al.
patent: 5101145 (1992-03-01), Rehm
Hamada Kaneyuki
Hamamoto Komei
Shibata Naotake
Kabushiki Kaisha Yaskawa Denki
Masih Karen
Shoop Jr. William M.
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