To easily and accurately control load in each of an upper and a lower motors to become equality by adjusting the difference between rotating speeds of the upper and the lower motors based on the difference between square values of both supplied currents so that the square values of the supplied current values to both the upper and the lower motors mutually coincide.
Since it can be considered that the difference between the rotating speeds of the upper and the lower motors 12, 14 and the difference between the loads in the upper and the lower motors 12, 14 show a simple corresponding relation and in a simple proportional relation as a rolling model and a motor characteristic, the difference between the rotating speeds of the upper and the lower motors 12, 14 is adjusted to keep the load balance of the upper and the lower motors 12, 14. Further, since it can be closely resembled that the rotating speed and the square value of the supplied current to the motor show the simple corresponding relation and are in the simple proportional relation as the characteristic in the single motor and the control becomes simple, the square values IU2, IL2 of the supplied current values in the upper and the lower motors 12, 14 are used to adjust the difference between the rotating speeds of the upper and the lower motors 12, 14.
OKAMURA YOSHIHIDE
UENO JUNICHIRO
MIYAJI KAZUHIRO
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